276 



CEPHALOPODA. 



embryos tins is not self-evident, as apparently different conditions are brought 

 about by' the intercalation of the yolk-mass and the superficial extension o 

 the germ The efferent aperture of the funnel does not appear to be directed 

 towards the mouth but rather turned away from it (Fig. 128 B). A com- 

 parison with the embryos of Loligo shows, however, that quite the same 

 conditions prevail in the two cases. If we imagine a LoUgo embryo, such as 

 the one seen obliquely from above in Fig. 117 B, p. 259, spread out flat, we 

 should find that the anterior aperture of the funnel is here also turned away 

 from the oral aperture which lies on the further side of the mantle and, apart 

 from the modifications peculiar to the LoUgo embryo, we should have a view 

 something like that given in Fig. 128 B. 



The further development of the Sepia embryo is characterised by 

 the fact that its superficial extension is arrested and it rises up from 

 the yolk-sac, the yolk then pressing in beneath the arched embryonic 

 rudiment; in this way, an internal yolk-sac is formed as already 



described for LoUgo. The rise 

 of the embryo from the yolk 

 is very gradual, and has a fairly 

 similar effect on the different 

 organs. Fig. 129 A-C repre- 

 sents a few stages in this 

 process. In the first two, the 

 embryo is seen from the oral 

 side. The posterior funnel - 

 folds (hit) at first still lie rather 

 far from the mantle, but the 

 latter, by extending laterally, 

 soon projects beyond them. At 

 the same time, the mantle 

 bends over and thus begins to 

 assume its final shape. 1 lie 

 embryo in its further rise from 

 the yolk is also followed by 

 the cephalic lobes and the 

 eyes, organs which, as in Loligo, 

 at this time and even later form 

 the largest part of the embryo 

 (Fig. 129 B). Fiff. 129 G, 



m.a 



OM 



Fig 130.— Older embryos of Sepia officinalis, 

 seen from the oral side (after Kolliker). 

 The yolk-sac, near the embryo ought to 

 be narrower. Lettering as in Fig. 129. 



representing the embryo at a somewhat later stage from the anal 

 side, shows its great resemblance in external shape to the 

 embryos of Loligo at about the stage depicted in Fig. 119, p- *>1. 

 The -ills are not yet completely grown over by the mantle; the 



