778 



ZOOLOGY 



SECT. 



extensive stomodseum eventually opens into this ; a proctodseum 

 is merely represented by the ectodermal pit forming the anus. 



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. 709, sli.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 

 the eyes ; and still nearer the vegetal pole a series of paired eleva- 

 tions, the rudiments of the arms. 



After the complete enclosure of the yolk by the blastoderm, the 

 mouth (mo.} is developed as an oval depression between the rudi- 



"tn 



FIG. 712. Two late stages in the development of Loligo, seen from the funnel side. Letters 

 as in preceding figures. (After Korschelt and Heider.) 



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

 appear two short ridges, the beginnings of the gills (cten.), and 

 a pair of folds the posterior funnel-folds (post. f. /.) 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.f.) developed further 



