"•:\ BLOPMENT OF SEPIA. 



275 



"» development of Sepia (Fig. 128 B) consists for a time in the 

 ^ rther g™ tf>of ^the rudiment, of the organs already present. The 



covers the gills, only parts of which project from beneath it (Fig 



"' ''• k) \ ' , ';'. ™ diment of th * -nus (a) appears between the gills. 



A depress^ which at first is crescent-shaped appears on the opposite 



%«* e 7f e ^ ulteat ^ edge of the germ-disc; thisTs the 



The /W>bW. also deserve mention. They have now united, 



"<<1 the principal parts of the 



funnel can ahvady be made 



out in them, viz., the anterior 



folds (vtf) which yield the chief 



part of the funnel, the lateral 



parts (nuchal muscle, km) which 



run back to the nuchal cartilage 



(nk) and, finally, the retractor- 

 folds (rf) which run towards the 

 gills. These parts are, indeed, 

 far less distinct than in Loligo 

 (Fig. 117 A and B, p. 259), 

 but are nevertheless homologous 

 with the similarly named struc- 

 tures found in that genus. The 

 origin of the funnel from two 

 halves is, on the other hand, 

 more distinct, that organ being 

 formed here, as in Loligo, 

 through the rising of the two 

 anterior folds which, after 

 obtaining in this way an increase 

 of surface, bend toward one 

 another and fuse (Fig. 129 (?) 



FiG.129.-Germ-discs and embryos of Sepia 

 officials, lying upon the yolk-sac. I 

 and /,, seen from the oral side ; (J, from 

 the anal side (after Kolu KER ). „ ,. 

 arms; an eyes ; ds, yolk-.,,; ,/, tj'. 

 hm nuchal muscle ; htf, posterior funnel 

 tolds; k, gills; Ja, cephalic lobes; Jes 

 germ-disc; m, mouth; ^.mantle oi 

 otocyste; rt, retractor of the siphon- 

 vtf, anterior funnel-folds. 



l.o principal part of the funnel derived from two half tubes 

 tln.s comes to lie in front of the mantle ; its posterior aperture is 

 turned toward the latter and opens into the mantle-cavity after the 

 mantle has grown over the funnel. The narrow anterior aperture 

 is turned away from the mantle. 



In adult Cephalopods, the efferent aperture of the funnel is directed to 

 wards the mouth, for the funnel lies on the ventral surface between he a n a l 

 and oral apertures (Figs. 120 and 121, p. 262). In the early stages of ££ 



