344 EYCLESHYMER, [Vol. X. 



PAGE 



8. The Mesoblast in Fishes 384 



9. General Considerations 386 



10. The Neural Folds in Amblystoma 393 



11. The Optic Vesicles in Amblystoma, Necturus and Rana.. 394 



12. The Olfactory and Oral Grooves in Rana 398 



13. The Paraphysis and Epiphysis in Amblystoma 399 



The following work was begun at Clark University in the 

 autumn of 1892, and continued during the succeeding summer 

 in the Marine Biological Laboratory at Woods Holl. Since 

 that time it has been carried on in the Zoological Laboratory 

 of the University of Chicago. 



An attempt to express my gratitude to Professor C. O. Whit- 

 man, at whose suggestion the study was undertaken, and whose 

 criticism has ever been a source of inspiration, would indeed 

 prove futile and sound extravagant. 



The intention was at first to study certain phases in the 

 ontogeny of Amblystoma punctatum (Baird), but the work has 

 been gradually extended so as to include a comparison of par- 

 ticular features of development in Necturus, Rana, Petromyzon, 

 Amiurus, Lophius, and Coregonus. 



I am indebted to Professor C. O. Whitman for Necturus 

 material, to Dr. W. M. Wheeler for Rana palustrus, to Dr. 

 H. P. Johnson for Petromyzon, to Mr. A. D. Mead for Lophius, 

 and to Professor J. E. Reighard for Amblystoma tigrinum. 



Habits, Oviposition, etc. — Amblystoma is probably the most 

 widely distributed of all the Urodela, being found in nearly 

 every state of the Union, as well as in Canada and Mexico. 

 For its systematic position the reader is referred to the works 

 of Cope, Hay, Garman, and others. 



For observing the aquatic habits of these animals early spring 

 is most favorable, since at this time they migrate to the ponds 

 where the eggs are deposited. The time of their appearance 

 varies in different localities. For the past four or five years, 

 in the vicinity of Ann Arbor, Mich., they have appeared regu- 

 larly on or about the 22d of March. At Worcester, Mass., I 

 found eggs, presumably of Amblystoma punctatum, on April 6, 

 1892, while in eastern Wisconsin the animals were observed 

 April 15, 1891. 



