4i8 



Harry Beal Torrey. 



which it has secreted and which is continuous with the egg case. 

 As we have seen, the hydroid never loses its power of locomotion, 

 even after the development of the filaments of the hold-fast. 



As the embryo leaves its egg case, it elongates, and an anterior 

 (oral) end can be distinguished from the narrower posterior 

 (aboral, proximal) end. The anterior end soon elevates itself, 

 and the embryo now touches the substratum by one side of the 

 aboral region only. 



For about thirty hours, or up to the time when the hydranth is 

 beginning to form, the embryo is completely covered by an 



Fig. 5. 

 Young Corymorpha. 



extremely delicate layer of perisarc. From this time the perisarc 

 is frequently limited entirely to the stem. Before the formation 

 of the hydranth, the perisarc covering the anterior end of the 

 embryo, and secreted by glandular cells of the ectoderm, is not 

 permanent, being dissolved as the stem progresses, probably by 

 the secretion of other cells in this region. As the hydranth begins 

 to develop, its ectoderm ceases to manufacture perisarc, which 

 henceforth is deposited by cells beginning at the aboral limit of 



