802 



ZOOLOGY 



SECT. 



merits of the eyes. Immediately in front of the edge of the mantle 

 appear two short ridges, the beginnings of the gills (den.), and a pair 

 of folds — the posterior funnel-folds (post.ff.) — which are formed 

 between these and the eyes, are the first rudiments of the funnel, 

 the greater part of which, however, is formed from a second pair 

 of folds — the anterior funnel-folds (ant. f. /.) — developed further 

 forwards. Behind the anterior funnel-folds appear two pit-like 

 depressions, which subsequently develop into the statocysts. 



The elevations on which the eyes {eye) are situated become 

 more and more prominent. The eyes themselves are formed 



dcTV 



Fig. 703.— Two late stages in the development of Loligo, seen from the funnel side. Letters as 

 in preceding figures. (After Korschelt and Heider.) 



from a part only of these elevations ; each is a pit which sub- 

 sequently becomes closed to form a vesicle — the optic vesicle : 

 later an ingrowth of the ectoderm over this gives rise to 

 the lens. 



The embryo covers only a part of the egg, and as it develops, it 

 withdraws itself more towards the animal pole, at which the 

 germinal disc was originally situated — a constriction, which soon 

 becomes very deep, separating it off from the rest of the egg ; the 

 latter, consisting of the greater part of the yolk enclosed in a thin 

 layer of blastoderm, forms a rounded appendage of the embryo — the 



