12 Bashford Dean hiemorial Volume 



in wide contrast all along the line to the development of the lampreys. Thus the hag- 

 fish eggs were so packed with yolk that the cleavage planes were confined to one end of 

 the egg as in the sharks, in contrast with the total or holoblastic cleavage of the lamprey 

 egg. He also showed that the development ot the hags is direct, so that the newly hatched 

 larval hags are far more like their elders than is the case with the larval lampreys, which 

 differ radically from the adults. 



From the fact that in these and other features of their development the hags differed 

 from the lampreys almost as much as the amphibians do from the sharks, Dean concluded 

 that the hags and lampreys must belong to two stocks which have been separated from 

 each other for long geologic periods, an opinion which in the light of Stensio's recent 

 studies becomes all the more probable. His papers on this subject abound in critical and 

 constructive comments on such classic problems as the behavior of the cells during the 

 differentiation of the primary germ layers, the relations between the branchiomeres and 

 the cephalic segments, and the supposed parallelism between individual development and 

 phyletic history. As to this last topic, if, under the influence of von Kupffer, in whose 

 laboratory he had worked, he had ever taken the doctrine of Recapitulation too literally, 

 his observations on the development of the hagfishes, as well as his other embryologic 

 studies tended rather to emphasi2;e the physiologic necessities of the developing organism 

 under the stress of a new environment; too close an adherence on the part of the embryo 

 to the theory of Recapitulation might well be a costly luxury, while on the other hand the 

 more pressing physiological needs of the embryo acted as premiums or rewards for short 

 cuts, accelerations, and new larval adaptations, so that the recapitulative background 

 became badly obscured. 



Dean's Bdellostoma material was also studied by one of his students (C H. Stockard) 

 who published a paper in which he defended the thesis that the so-called tongue of the 

 cyclostomes was not homologous with the true tongue of higher fishes but represented 

 the fused mandibular arches of the gnathostome chordates. But by far the greater part of 

 the organogeny of the hagfish, as revealed in Dean's Bdellostoma embryos remains to be 

 described. It is therefore gratifying to state that several years ago Dr. Dean handed over 

 much of this material to Dr. J. Leroy Conel, of the Boston University School of Medicine, 

 who is studying in it the development of the brain. 



STUDIES ON THE BEHAVIOR OF LARVAL AND ADULT FISHES 



1896-1912 



Dean never lost an opportunity to observe at first hand either the spawning and 

 nesting habits of lampreys, garpikes, Amia, and other fishes, or the behavior of the newly 

 hatched larvae in reference to food reactions, mode of locomotion, etc. Observations on 

 such topics were incorporated in all his larger papers on development, but m a number of 

 cases were set forth in brief articles. Thus, in 1896 he published a brief abstract of notes 

 on the behavior and food-taking of newly hatched A7nKi and the feeding habits of larval 

 J^ecturus; in 1898 appeared a paper (with Francis B. Sumnerj on the spawning habits 



