Twenty-fifth Annual Meeting. 71 



lected by us from the Ohio river the summer previous, he found unmistakable evi- 

 dences of a callosum in the bony fishes. Our best morphologists have hitherto been 

 unanimous in describing the fish brain as lacking the callosum. The common drum, 

 Haploidonotiis, however, has this commissure well developed.* My friend, Mr. C. H 

 Turner, has also found the callosum in several groups of birds, where its presence 

 had not hitherto been suspected. t The other great commissures of the brain have 

 been studied with results quite as satisfactory. If space permitted, we might dwell 

 on the philosophical significance of these facts; sufiice it to say, that the homol- 

 ogizing of the commissures of the brain is a long step in the direction of a solution 

 of the vexed question of the segmentation, or metamerism, of the head — a step, too 

 which once surely taken, might lead directly to that solution. 



The so-called "pineal gland" has been the subject of active discussion from the 

 day that Spinoza declared it to be the seat of the soul until now. Here, too, the 

 comparative method has borne good fruit. Whatever its present function, (and 

 there are nearly as many opinions here as there are authors,) its origin seems clear. 

 It is present in all vertebrates, and in the lower is more perfectly developed than in 

 the higher. Moreover, it is larger and more perfectly developed in the young than 

 in the adult. These points show that its significance is to be sought in the past 

 rather than the present. It is now several years since the bold suggestion was haz- 

 arded that it formerly functioned as an eye. Of this, the evidence grows yearly 

 more conclusive. Alborn, on petromyzon.J Herrick, on the lizard and black snake,§ 

 and many others, find evidence of a degenerate retinal surface in the pineal body? 

 while Hitter, in a paper on "The Parietal Eye in Some Lizards from the Western 

 United States," describes \ a pigmented retinal epithelium in the pineal body, and 

 in the same vesicle a rudimentary lens and other evidences of the so-called parietal 

 eye. Appearing at almost the same time in the American Journal of Science, (Feb- 

 ruary, 1891,) is Professor Marsh's description of the skuUs of certain North Ameri- 

 can fossil reptiles, the Dinosaurs, with a large "parietal foramen," an opening in the 

 top of the head at the union of the parietal and squamosal bones. This he regards 

 as the socket of a "pineal eye." 



In the fishes there is great modification of the relations. The compact, conical 

 body of the mammals is represented by a very slender tube, with walls consisting of 

 a single layer of epithelium. This tube passes up toward the top of the cranium, 

 which, however, we are told it never reaches.*! Whatever may be the relations in 

 the adult teleostean brain, they are certainly not as described in the case of the 

 young. I have sections of a young catfish one inch long, cut through the entire 

 body, which show this tube very clearly passing up to the skull and spreading out 

 to form a closed sac, which I have no hesitation in saying is the rudiment of a primi- 

 tive optic vesicle. The skull, too, at this point is considerably thinner than in the 

 adjacent regions. 



Of supreme importance in all matters which concern the origin of nerve cell and 

 nerve fiber, is a recent paper, by Prof. Wm. His, on "Histogenesis and Combination 

 of Nervous Elements."** The nervous system, at an early embryonic stage, consists 

 of a simple tube, running the entire length of the body, with walls of single-layered 

 columnar epithelium. This relation persists in the adult, and is the basis of the 



*Ibid., December, 1891. 

 tibid, March, 1891.. 

 iZeits. f. Wiss. Zoologie, XXXIX. 

 g Jour. Comp. Neurology, I, pp. 27, 28. 

 \, Bull. Mus. Comp. Zoology, January, 1891. 



•^ Wiedershelm's Comparative Anatomy, Eng. tr., p. 142; and, in the case of the catfish, by Professor 

 Wright, in the Proceedings of the Canadian Institute, vol. II, p. 363. 



** Histogenese und Zusammenhang der Nerven-Elemente, Archlv. f. Anat. und Phys., 1890. 



