94 PART I. GENERAL ACCOUNT 



enucleate mass — the cytophore; the cells come to lie on the surface of this 

 cytophore into which their cytoplasm seems to merge (Fig. 62B). At the 

 spermatid stage the germ cells are still joined into morulae or spermato- 

 spheres (Fig. 62 C). A short time after the sperm are formed they become 

 detached from the cytophore. The ripe sperm are filiform and consist of 

 thread-like deeply staining heads and long tails (Fig. 62D). 



Sometimes early stages of spermatogenesis appear to predominate in the 

 anterior part of the sperm sacs, though usually all stages are mixed together 

 and may be encountered at all levels. It remains quite unknown whether 

 compact groups of gonocytes forming some sort of germinal epithelium are 

 to be found in some place on the walls of the anterior part of the sacs. 



Thus it is clear that these organs are true sperm sacs. In a general way they 

 recall the sperm sacs of oligochaetes and leeches and, as in these annelids, 

 they represent specialized portions of the coelom ; their walls appear to be a 

 variety of coelomic epithelium. The general nature of the fluid filling the 

 cavity, with the characteristic spermatospheres or morulae, also recalls the 

 contents of the sperm sacs in oligochaetes and leeches. 



The ciliated bands on the walls of the sperm sacs apparently serve to 

 circulate the fluid containing the germ cells, and the cilia covering the sides 

 of the anterior part of the sperm sac presumably serve also to propel the 

 clumps of ripe sperm into the spermducts. The presence of a common boun- 

 dary between the sperm sacs and the dorsal blood vessel ensures a richly 

 sufficient supply of nutriment for the developing germ cells. 



The spermducts 

 The front end of the sperm sac communicates with the corresponding 

 spermduct which first runs backwards to form a loop before turning forwards 

 alongside the mesentery to the border between the mesosoma and the 

 metasoma where it turns down onto the ventral side to open to the exterior 

 through the genital papilla of that side (Figs. 9, 15, 60). The spermducts are 

 thick-walled epithelial tubes, furnished externally with a thin layer of muscle 

 fibres and peritoneal epithelium, and attached to the ventral body wall by a 

 delicate mesentery (Fig. 64). The histological structure of the walls varies 

 considerably in the different regions. Thus in Lamellisabella zachsi, near the 

 point of attachment to the sperm sac the epithelium of the spermduct 

 consists of tall ciliated cells which are remarkable for details of the structure 

 of the ciliary roots. The root-threads run from the basal granules of the cilia 

 and form, as a rule, a characteristic cone, gathered together into a rather 

 stout bundle which extends to the basal end of the cell where it diverges 



