212 K. :\[ITSUKUEI AND C. ISHIKAWA. 



Chelonia sinre tlie dnys of Agassiz and Clark, and therefore with 

 mordern methods of investigation. Mr. Hattori kindly consenting, we 

 went to his farm daily during tlie breeding season of 1884 and of 1885, 

 and succeeded in collecting a fairly ccmiplete series of the Tryonix 

 embryos, beginning with the titne wlien the eggs are deposited, and 

 ending with their hatching out. The present paper gives the results 

 of our study on the formation of the germinal layers. Papers on other 

 points and later stages of development will follow from time to time 

 since the investigation is being continued, as the pressure of other 

 duties permit us. 



We wish to return our warmest thanks to Mr. Hattori for cheer- 

 fully acceding to our numerous demands on his good nature, and for 

 furthering greatly our work with his intelligent assistance. Thanks 

 are also^iue to the authorities of the University of Tokyo for the pay- 

 ment of necessary expenses attending the investigation, and for the use 

 of instruments, reagents, &c. Finally, we wish to express our deep 

 obligations to Dr. Isao Jijima for valuable suggestions in regard to the 

 methods of investigation. 



We made many interesting observations on the breeding habits of 

 Trionyx, but we reserve these for some other occasion, as foreign to 

 the purpose of this paper. We simply mention that the Trionyx eggs 

 are nearly spherical in shape, and have a hard brittle shell like that of 

 the fowl, and not leathery, as in some Chelonia. Their size is very 

 variable, the smallest we measured being 10 mm., the largest 23 mm., 

 the most usual size about 21 — 22 mm. in diameter. This difference 

 in size seems to be due mostly to the size of the parent. A¥ith this 

 we pass on at once to the consideration of the subject proper of the 

 present communication. 



The earliest stage of which we will give a detailed description is 

 taken froni an egg opened directly after its dept^'-iition. Oar attempts 



