NEMATELMINTHES. 373 



canal, and soon becomes divided into an cesophageal section 

 (fig. 1 66 F, ci') formed of granular cells, and a posterior division 

 formed of clear cells. The mesoblast (fig. 166, me) takes its 

 origin from certain special hypoblast cells around the mouth, 

 and thence grows backwards towards the posterior end of the 

 body. 



The young Cucullanus becomes hatched while still in the 

 generative ducts of its parent, and is distinguished by the 

 presence of a remarkable thread-like tail. On the dorsal surface 

 is a provisional boring apparatus in the form of a conical papilla. 

 A firm cuticle enveloping the body is already present. In this 

 condition it leaves its parent and host, and leads for a time a 

 free existence in the water. Its metamorphosis is dealt with in 

 another section. 



The ova of the Oxyuridae parasitic in Insects are stated by Caleb (No. 

 386) to take the form of a blastosphere at the close of segmentation. An 

 inner layer is then formed by delamination. What the inner layer gives rise 

 to is not clear, since the whole alimentary canal is stated to be derived from 

 two buds, which arise at opposite ends of the body, and grow inwards till 

 they meet. 



The generative organs. The study of the development of 

 the generative organs of Nematodes has led to some interesting 

 results. In the case of both sexes the generative organs origi- 

 nate (Schneider, No. 390) from a single cell. This cell elongates 

 and its nuclei multiply. After assuming a somewhat columnar 

 form, it divides into (i) a superficial investing layer, and (2) an 

 axial portion. 



In the female the superficial layer is only developed dis- 

 tinctly in the median part of the column. In the course of the 

 further development the two ends of the column become the 

 blind ends of the ovary, and the axial tissue they contain forms 

 the germinal tissue of nucleated protoplasm. The superficial 

 layer gives rise to the epithelium of the uterus and oviduct. 

 The germinal tissue, which is originally continuous, is interrupted 

 in the middle part (where the superficial layer gives rise to the 

 uterus and oviduct), and is confined to the two blind extremities 

 of the tube. 



In the male the superficial layer, which gives rise to the epi- 

 thelium of the vas deferens, is only formed at the hinder end of 



