204 



CEPHALOPODA. 



is shewn at m and the anal immediately in front of an. The gills, nearly 

 covered by the mantle, are seen at br. At p are the cephalic swell- 

 ings, and the eye is seen at oc. The arms 1 5 form a ring 

 outside these parts. The whole of the embryo, with the exception of 

 the gills, the funnel, and the outer border of the blastoderm, is 

 richly ciliated. 



The embryo up to this time has had the form of a disc or saucer 

 on the surface of the yolk. After this stage it rapidly assumes its 

 permanent dome-like form, and becomes at the same time folded off 

 from the yolk. The blastoderm is very slow in enveloping the yolk, 

 and the whole yolk is not completely invested till a considerably 

 later stage than that represented in fig. Ill B. As soon as the 

 blastoderm covers the yolk-sack cilia appear upon it. The mantle 

 grows very rapidly, and its free border soon projects over the funnel 

 and gills. After the two halves of the funnel have coalesced into 

 a tube, it comes to project again beyond the edge of the mantle. 



On the completion of the above changes the resemblance of the 

 embryo to a Cuttle-fish becomes quite obvious. Three of the stages 

 in the accomplishment of these changes are represented in fig. 112. 



To the ventral side of the embryo is attached the enormous 

 external yolk-sack (yk), which is continuous with an internal section 



oc 



FIG. 112. 



SIDE VIEWS OP THREE LATE STAGES IN THE DEVELOPMENT OF SEPIA. 

 (After Kolliker.) 



m. mouth; yk. yolk-sack; oc. eye; int. mautle. 



situated, within the body of the embryo. The general relations of 



