800 



ZOOLOGY 



SECT. 



inesenteron. From whatever source it may be derived, the latter 

 becomes distinguishable as a cell-plate which is converted 

 into a vesicle opening below against the yolk-epithelium, there 

 never being any direct communication with the yolk. An exten- 

 sive stomodseum eventually opens into this ; a proctodasum is 

 merely represented by the ectodermal pit forming the anus. 



l''i' ;. 700. Early stages in the development of Loligo A, stage at which the rudiments of the eyes 

 and of the shell-gland are first distinguishable ; B, later embryo from the oral side ; 6' and D, 

 from the anal side, riiit. ./'. ./'. anterior funnel-fold; nr. rudiments of arms; rten. ctenidia ; 

 -I' . eye , //<'->. mouth ; mnt. rudiment of mantle ; ot. statocyst ; post. f. /. posterior funnel-fold ; 

 .-//. til. shell-gland ; yk. s. yolk-sac. (After Korschelt and H eider.) 



About the middle of the blastoderm appears a' thickening 

 of a cap-like shape, the edges of which become raised above the 

 general level of the blastoderm ; this is the rudiment of the 

 mantle. On the surface of this is developed a depression which 

 subsequently forms a closed sac the shell-gland (Fig. 700, sh-.gl.). 

 Below the mantle i.e. nearer the vegetal pole appear two eleva- 

 tions each with a pit-like depression, which are the rudiments of 



