DEVELOPMENT OF SEPIA. 



275 



They have now united, 



The development of S^>in (Fig. 128 h] consists for a time in the 

 further growth of the rudiments of the organs already present. The 

 edge of the mantle begins to rise from the germ-disc, and already 

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

 128 B, k}. The rudiment of the anus (a) appears between the gills. 

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

 side of the mantle, quite at the edge of the germ-disc ; this is the 

 oi'nl '(/H-rttire (HI). 



The funnel-folds also deserve mention, 

 aid the principal parts of the 

 funnel can already be made 

 out in them, viz., the anterior 

 folds (-I'tf) which yield the chief 

 part of the funnel, the lateral 

 parts (nuchal muscle, hm) which 

 run back to the nuchal cartilage 

 (/*/) and, finally, the retractor- 

 folds (rt) which run towards the 

 gills. These parts are, indeed, 

 far less distinct than in Loligo 

 (Fig. 117 A and J5, 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 Lolif/o, 

 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 C). 

 The principal part of the funnel derived from two half tubes, 

 thus 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 the anal 

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



FIG. 129. Germ-discs and embryos of Sepia 

 qjficinalif, lying upon the yolk-sac. A 

 and B, seen from the oral side ; C, from 

 the anal side (after KC^LLIKER). a r a 6 , 

 arms ; au, eyes ; ds, yolk-sac ; /, fins ; 

 hm, nuchal muscle ; htf, posterior funnel- 

 folds ; k, gills ; kl, cephalic lobes ; ks, 

 germ-disc ; m, mouth ; ma, mantle ; ot, 

 otocysts ; rt, retractor of the siphon ; 

 vtf, anterior funnel-folds. 



