the hard tissues of animals, such as the bones in vertebrates, and the axial rods in various invertebrates, to undergo transverse segmentation; to the tendency of portions of such rods to be twisted. upon themselves; to the causation of articulations, etc. I deemed it my province to direct the attention of medical students to the importance of these topics, and, with the object of making the series of direct value to them, drew my illustrations, whenever practicable from human anatomy, physiology and pathology. A separate group of subjects was next treated. It embraced the themes of Variation, Teratology, Compensation, etc. In this group instances of variation in the human subject were taken up, described and explained. The object of this series was to awaken interest in the study of variations of human anatomy as met with in the dissecting room or the practice of medicine, and to enable the medical man properly to appreciate and describe the various congenital monstrosities that may come under his notice. In addition to these I usually gave one lecture on the medico-legal value of a knowledge of the skeleton (pointing out the characteristics of the bones of the different classes of vertebrates as determined by the study of fragments of bone) as well as one on medical credulity. In illustration of which subject, I pointed out fallacies in medical observation. Every physician, who has become identified with biological studies, can mention many instances in which his services as expert have been requested upon subjects as simple in their nature, as the error in observation has been gross and mortifying. It will be remarked that the medical emphasis is everywhere insisted upon in a course of lectures such as that which has been briefly outlined. Would it not be entirely improper to attempt the delivery of such a course, before classes of young men in the literary departments of our colleges? Doubtless instruction. in comparative anatomy as a branch of general education, or one preparatory to medicine, is of great value. But I am anxious that such a course should not be held to be identical in character with the one I have thus described. The student who proposes to attend, to the best advantage, a course of such lectures should already have attended a general course in biology, and have familiarized himself with the rudiments of human anatomy and physiology. It has been commonly said to me by my students-most of whom had already studied two years-that the lectures were difficult to follow. If it so proved to advanced pupils, it is easy to foresee what would be the result of lecturing on such basis to classes preparing themselves for matriculation, or even for studies of the second year. The explanations of the generalizations of biology, the varieties of human anatomy, the abnormalities of structure involving the most abstruse problems in biological science-cannot be essayed with advantage to other than advanced students. I have again and again stopped in the course of a demonstration and remarked that if there were any gentlemen present who felt themselves to be imperfectly prepared upon the human anatomy of the subject under consideration, such had best retire from the lecture room for it would prove for them a waste of time to remain. It was my custom to name at the close of each lecture the subject of the next --to invite special attention to the points to be therein treated--and to request my pupils to consult their text books before reporting for the lecture. By this plan I was free from the necessity of first demonstrating the anthropomorphic features before taking up the comparative. The conviction that remains after having given much thought to the matter is, that the outline of the structure of animals as taught in our colleges of general education, or, in preparation for the special medical course, does not meet the end in view, but that a supplemental course should be given after the first or second session. If the time of the curriculum does not permit such instruction, one of two ways is open -- either to make the course post-graduate or to lengthen the session. This is a matter of detail which need not interfere with the main point I advocate, i. e., that the kind of comparative anatomy a student of medicine needs cannot with advantage be offered him until he is advanced in his special studies. PLAN OF THE CEREBRO-SPINAL NERVOUS SYSTEM.1 [ABSTRACT.] By S. V. 1. The primitive sense is tactile and all senses have proceeded from its differentiation. For illustrative purposes let us consider energy as divided into molecular vibrations, from one ethereal pulsation in an eternity, to an infinite number of vibrations in one second. In such an undulatory series we may see, as a small division of it, all forces from sound to gravitation represented. While the protozoön may be visibly affected by every such undulation the homogeneity of its composition prevents any differential response; for instance, the tremor of a musical note, heat, light, electricity, alike produce contractions or expansions (motions) of its mass. In a higher form of life nerve tissue appears, which conveys only certain vibrations and rejects all others. Take one undulation in a second as the capacity of this nerve fibre. It is a tactile nerve. When a nerve-fibre conveys more rapid undulations differentiation begins. Sixteen to forty thousand per second begin and end the auditory vibrations. Quicker vibrations to four hundred and fifty billion per second we may view as heat appreciation, thence to eight hundred billion from red to violet light, above this fluorescent undulations, "chemical energy," electricity, to infinity. We may thus mathematically conceive an auditory sense derived from the general tactile or a special touch sense (like that of the fifth pair of nerves). An optic sense would arise from this same tactile, and we have seen it thus differentiated embryologically. 2. Qualitative differentiation of the nervous organization proceeds dorsally, with a tendency toward the head end. That portion of the animal which stands in most direct relation to the changing molecular movements of the environment develops the highest sensory and motor nerve-centres and projections. 3. Repetition of parts of a system, up to a certain point, ceases; and these parts become commissurally united before another system is perfected. The sympathetic nervous system, consisting of the intestinal 1This paper is printed in full in the Journal of Nervous and Mental Disease, Oct. and vascular or vaso-motor nerves, develops first. Schenck and Birdsall (Archives of Medicine, vol. I, No. 2), on the Embryogeny of the Sympathetic, consider this system as composed of masses originating in the central nervous system. This is a truth from one standpoint, and that a very narrow one. Blending the results of comparative embryology and anatomy, the sympathetic precedes the creation of other systems. The second system to appear phylogenetically is the spinal, equivalent in the invertebrates to their "cerebral" ganglia. The third system is the intervertebral, the swellings upon the posterior roots of the spinal nerves. 4. The cerebellum is formed from fused hypertrophied intervertebral ganglia. Many sensory cranial nerves pass through this organ and by the fusion of these originally separate centres coördination occurs necessarily. Excessive development on the one hand, or want of development on the other, places all the ganglionary tubercles and lobes of the encephalon in the third system category. Thus the præ-frontal lobe of the cerebrum, the occipital and temporal lobes, the olivary body, the olfactory lobe, the mammillary eminence, the epiphisis cerebri, the tubercula bigemina, the petrosal and Gasserian ganglia were originally intervertebral ganglia, and still maintain resemblance to these ganglia in many particulars. 5. The præ-frontal lobe is the last intervertebral ganglion to develop. It grows larger in the scale of intelligence and presses the occipital (see the brains of monotremes and marsupials) backward, downward and forward, thus forming the temporal (or what has been erroneously termed the middle) lobe. 6. The cerebro-spinal nerves, in some cases, preserve their original projections from and to muscles, but these nerves may also have not only a distribution to the viscera, as has the pneumogastric, but may also project into and from other system-centres. The lateral columns of the spinal cord, the tegmentum and crura cerebri in their main mass may thus be regarded as cerebro-spinal nerves of the highest series, having lower system-centres for peripheries. The præ-frontal lobes thus exert an inhibitory control over the highest centres, because such centres are peripheries for the nerves of these foremost ganglia. EVIDENCES OF THE EFFECT OF CHEMICO-PHYSICAL INFLUENCES IN THE EVOLUTION OF BRANCHIOPOD CRUSTACEANS. BY CARL F. GISSLER, of Brooklyn, N. Y. DURING the winter months Eubranchipus vernalis Verrill 2 occurs near Maspeth, Long Island, in immense numbers in large communicating ponds containing clear, yellowish fresh water. In January last I found, in a small and entirely isolated pool, less than a hundred paces from the above mentioned place, a number of perfectly colorless, smaller, but sexually mature individuals of branchiopod Crustaceans. The bottom of the pool is a white and very soft clay and the water itself is of a milky color. I collected a number, and observed the following characters: A. Very few individuals of both sexes bearing, with the exception of transparent body, and the red furca 3 of the post-abdomen, the same characters as Eubranchipus. B. A great number of colorless individuals from 15 to 22 mm. in length. These differ from the larger, red Eubranchipus in the following particulars: Cephalic scute large and convex. Basal joint of male clasper cylindrical. Claspers crossing each other, short, tip of second joint with a blunt, minute tooth. Second joint more or less conical, tapering. A number of full-grown forms between sets A and B occurred, evidently transitory stages. I expect soon to give an account in Dr. Packard's Monograph on Phyllopod Crustacea, of the sexual organs (to be illustrated by a plate), copulation and the biology of these colorless individuals. C. A single specimen of male Chirocephalus.5 D. A hermaphrodite. Sexual organs separate, both male and female claspers present. 6 E. A single male individual with a minute tooth on the second joint of its right clasper, tooth wanting on the left. Left clasper in normal position, right clasper twisted around, thus apparently 1 From January till April. 2. Observations on Phyllopod Crustacea of the family of Branchipide with descrip. tions of some new genera and species," by Prof. A. E. Verrill, 1869. 3 The normal red Eubranchipus has a white furca. Pale specimens of Strepto. cephalus Watsoni Pack. have also a red furca. F. Spangenberg's paper in Zeitsch. f. wiss. Zool., XXV, Supplem. 1875, p. 14. Proved to be a very large specimen of Chirocephalus Holmani Ryder. March 22, 1881, I found a large pond between Glendale and Ridgewood, Long Island, densely populated with both Chirocephalus Holmani Ryder and Eubranchipus vernalis (normal). The former is described in Proceed. Acad. Nat. Sciences of Philad., 1879, p. 200. * I described it in American Naturalist, February, 1881. The claspers are the second pair of antennæ, transformed into auxiliary copu lation organs. |