The hypoblast of the embryo gives rise to the alimentary canal, and soon becomes divided into an oesophageal section (fig. 166 F, _oe_) 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 Oxyuridæ parasitic in Insects are stated by Galeb (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 originate (Schneider, No. 390) from a single cell. This cell elongates and its nuclei multiply. After assuming a somewhat columnar form, it divides into (1) a superficial investing layer, and (2) an axial portion. In the female the superficial layer is only developed distinctly 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 epithelium of the vas deferens, is only formed at the hinder end of the original column. In other respects the development takes place as in the female. Gordioidea. The ovum of Gordius undergoes a regular segmentation. According to Villot (No. 391) it forms at the close of segmentation a morula, which becomes two-layered by delamination. The embryo is at first spherical, but soon becomes elongated.