THE DEVELOPMENT OF ADMETUS PCMTLIO. 609 



pit/' as it was in the last. The '^ surface pit" also 

 resembles the last described in having a slight depression on 

 its surface. The cells of the epidermis also take an active 

 part in the building up of the groups, by forming a funnel- 

 like sheath around the radial fibres. The nuclei of the cells 

 forming this sheath measure about "018 mm. in length by 

 •005 mm. in breadth. Karyokinetic figures are sometimes to 

 be found in them. 



The next such collection of germ-cells is, perhaps, even 

 more typical. It lies just at that point where the abdomen 

 forms an angle to the cephalothorax (fig. 8). Although 

 more advanced, than the last its dimensions are not larger. 



The length and breadth are the same as those of the last 

 group, the length of the radial fibres being '02 mm., as in the 

 last case; the group, however, now lies "037 mm. from the 

 surface. 



The cause of the group lying deeper than the last described 

 is an ingrowth of the epidermis in the shape of a narrow 

 tube. Its bore is "007 mm., and its length '01 mm. The 

 walls of this tube are formed by a single layer of cells, 

 Avhose nuclei are but lightly stained, and which contain very 

 larsfe micro-nuclei. One nucleus I measured was '01 mm. 

 long by '004 mm., its micro-nucleus, however, actually 

 measuring '004 by '003 mm. 



The nuclei of the cells forming this tube are all arranged 

 with their long axes lying at right angles to the axis of the 

 tube. The tube ends in an expansion, forming a nearly 

 spherical sac, whose diameter is about '01 mm. The walls of 

 this sac are formed by the ends of the radial supporting 

 fibres. The sac just described lies within the funnel-shaped 

 sheath, which encloses the radial supporting fibres. The 

 next group of cells so much resembles the last described 

 that it is not necessary to go into any details about it. 



Still proceeding forwards, we now meet with a group 

 which half retains its original form and independence, 

 and is half connected with and converted to the ventral 

 gangliou-cord in its definite form. The original germ-group 



