20 



K. MITSUKURT. 



illnstratiiiri- lliis ])r)i]it lliaii those, of ('Iciniiiys, I sliall hcoin with 

 the former species. 



Figs. 60-63 (PI. VII.) aiKl Figs. S7 mid 87« (Fl. X.) give 

 successive stages in the development of the ullantois in Trionyx. 



Fig. 60 is fr<:»m an embryo very simihir to the one represented 

 in Fig. 23 witli about seventeen mesoblastic somites. The sjjhmch- 

 noplenre has not vet l)een folded under to form the hind-gut. The 

 first trace of the allantois (All.) is, however, already visible as a 

 shallow notch in the posterior ]iart of the tail- lobe. In a surface- 

 view, this notcli appears as a shalh^w transverse slit as re))resented in 

 Fig. 20. Fi'om the first, tVic {)osterior wall of the allantois is lined 

 with a distinct epitlielium of the hy|iol)last. Its anterior wall is no 

 doubt also of the hypoblastic nature, but is her(^ fused Avith \\\v 

 indifferent cell-mass alx^ve it. 



Figs. CA-G?^ (IM. Vll.):uid Figs. 87 and 87« (Fl. X.) s])C'A suf- 

 ficientlv foi- themselves :ind need tioI be miiiutelv exphn'ncd to those 

 who ai'e alreadv familial' wiih llic (•<»! I'espoudiiig shigcs iii j>irds. 

 ]jv the gradual f )lding of the spianclmi^pleui'e on the ventral face, 

 the hind-gut is j)roduced, and on its ventral floor the allantois 

 becomes esta])lished as a vesicle at first wide open ahme (Figs. 62-63) 

 but with its gradual growth constricted at the neck (Fig. 87). Fig. 

 87« represents a cross-.se<'tioii of the alhuitoic region from an embryo 

 of the same stage as that represented in Fig. 87. It shows that the 

 cavity of the allantois is at this stage two-lobed. 



Figs. 64-66 (1^1. VII.) are three successive stages in the develop- 

 ment <^f the allantois in Clcuniiys. Althougli these do not give as 

 complete a series as in Trionyx, they are }'et sufficient to show that 

 the process in Clemmys is in all essential res])ects similar to that 

 in Trionyx. 



In none of my series of sections can I detect any trace of an 



