64 SUMMARY OF CURRENT RESEARCHES RELATING TO 



body, and, in life, is a circular orifice largely capable of extension and 

 contraction. The oesopbagus is narrow and tbin-walled ; the pharynx, 

 which is strongly muscular, may be elongated or shortened, or pro- 

 truded through the mouth ; in histological characters it agrees gene- 

 rally with the same organ in many Ehabdocoeles, e. g. Derostomum. 

 The intestine makes but feeble curves, and ends blindly at the hinder 

 end of the body. 



No less do the other characters — external covering, musculature, 

 and so-called body-parenchyma — tell the same story of zoological 

 af&nity. The ciliated body-epithelium is composed of polygonal 

 flattened cells, with finely dentated margins. Below this there is a 

 single layer of longitudinal fibres, and then one of circular fibres, 

 VFhich is likewise single ; none of the fibres have a nucleus, and they 

 are all very long and fine. The parenchyma is very feebly developed 

 on the hinder part of the body, or region of the true intestine ; 

 anteriorly it presents a cellular structure with a number of nuclei, 

 and between these, especially in the most anterior region, there are 

 large vesicular spaces, which permit of the contractions of the body 

 and the protrusion of the oesophagus, and copulatory organ. The body- 

 wall appears to be remarkable from being traversed by numerous 

 efferent ducts from small unicellular glands, which lie within the 

 musculature, and are to be regarded as modified epidermal cells ; they 

 are perhaps homologous with the rod-cells of other Turbellaria. 



The nervous system is in every way that of a typical Turbellarian ; 

 the cerebrum lies in front of the pharynx, above the oesophagus ; it 

 consists of three ganglia, which are not sharply separated from one 

 another ; one is median to the other two. The latter give off two 

 longitudinal nerves, which are altogether devoid of ganglionic cells, 

 and which very soon become thin ; they probably reach to the hinder 

 end of the animal. All these ganglia give off groups of ganglionic 

 cells anteriorly ; the dorsal series extend almost to the anterior end of 

 the body, while the lateral pass to the lateral pits of the head. The 

 brain of Prorhynchus is, then, to be distinguished only from that of 

 other Ehabdocoela by the fact that the commissure is covered by 

 ganglionic cells. The first-mentioned pits have a narrow orifice and 

 are somewhat pyriform in shape ; the longer cilia which invest them 

 are placed on a fringe formed by fused epithelial cells. Such pits are 

 known in certain Ehabdocoeles, e. g. Microstomum and Stenostomum, &c. 



Although Prorhynchus, like the majority of known Ehabdocoela, is 

 hermaphrodite, there is some reason for supposing that the male are 

 mature before the female products ; the male organs consist of a pro- 

 trusible penis, connected with a ductus ejaculatorius, which, after 

 coils that vary with the state of contraction of the animal, passes to a 

 thin-walled seminal vesicle ; the whole apparatus is ventral in position, 

 and ought not, therefore, for a moment to be compared to the pro- 

 boscis of the Nemertinea ; the male glands lie behind the vesicle, on 

 either side of the intestine, where they have the form of small rounded 

 follicles, without special walls ; they are filled with finely granular cells 

 of various sizes, intermixed with ripe spermatozoa. The larger of the 

 cells often contain two nuclei, and are peripheral in position; the smaller 



