ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 223 



gonads arc placed in the binder thoracic chamber. With these ana- 

 tomical and physiological differences are correlated certain local 

 differentiations of the nephridia. 



The whole number of the nephridia is proportionally small in the 

 Terebelloidea ; the anterior pairs which communicate by their internal 

 orifices with the cavity of the prediaphragmal segments have, ordinarily, 

 small infundibula, while their tubular excretory portion may attain con- 

 siderable dimensions; their function is exclusively excretory. In the 

 nephridia of the hinder thoracic segment the funnel is generally the 

 most prominent part, being often of enormous size; the ducts, on the 

 other hand, are poorly developed. These organs appear, therefore, to 

 be especially adapted for taking up finer bodies swimming in the ccelom, 

 and have the function of efferent ducts for the genital products ; with 

 this, they seem to lose their excretory function. All the nephridia of 

 the Terebelloidea open within the area of the somite to which they 

 belong, and they open to the exterior separately and independently of 

 one another ; their ciliated infundibula are always intersegmental in 

 position, and always open into the next preceding segment. In all these 

 worms the nephridia are confined to the thorax. 



After an account of his macroscopical and microscopical investigations 

 of Amphitrite rubra, Lanice conchilega, and Melinna palmata, the author 

 points out how greatly they differ from one another in the details ; we 

 may take it that, typically, the nephridia are developed in a moderate 

 number of pairs (about six) in continuous series, beginning from the 

 third segment ; but they may begin further back, or the series may be 

 broken by the loss of a pair; the presence of more than one pair of 

 nephridia in a segment is a rare occurrence. There are never more than 

 three pairs in the anterior chamber, the diaphragm being typically placed 

 between the fourth and fifth segment ; this position of the diaphragm is 

 characteristic of group A or of the Amphitritea, Polycirridea, Corepho- 

 ridea, and Trichobranchidea ; in group B, which consists of the Ampha- 

 retea and Amphictenea, there is only one pair of nephridia, the diaphragm 

 being placed between the third and fourth segments. In Pista cristata 

 alone has the complete absence of the anterior nephridia been noticed. 

 A relatively large number of hinder nephridia is rare, but there are 

 never less than two pairs. A tabular statement is given of the number 

 and arrangement of the nephridia found in the species which were 

 examined. 



As a rule the nephridia of either side are distinct from each other in 

 all Annelids, but in Lanice conclrilega and Loimia medusa there are 

 nephridial ducts, by means of which the organs of opposite sides are 

 brought into connection. 



The peritoneal glands and their products are next described ; these 

 are the gonads, the lymph-glands, and the pigmented lymph-glands. 



In discussing the functions of the nephridial system, Herr Meyer 

 states that iu AmpMtrite rubra he has found that the protoplasm of the 

 cells gives rise to two kinds of excretory products ; these are pigmented 

 crystalline concretions, and clear excretory fluid in vacuoles; and the 

 cells that produce them are found to be localized separately. As the 

 nephridial tubes are often surrounded by a close vascular network 

 belonging to their peritoneal investment, it is more than probable that 

 some of the excretory materials are obtained directly from the blood. 

 From what has already been said it is clear that there is a division 



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