ON TWO NEW GENERA OF AQUATIC OLIGOCH^ETA. 275 



from granules, and the interstitial cells seemed to be fewer in number than is ordinarily 

 the case. 



The transverse muscular layer is only about two fibres wide. The longitudinal 

 muscles consist, as in other of the lower Oligochseta, of a row of muscle-plates, indicated 

 in fig. 14. These show in transverse sections a disposition to curl up at the free edge. 

 Isolated fragments of the longitudinal muscle lamellae are illustrated in fig. 15. They 

 are darkly stained and show no recognisable fibrillation. 



§ Nephridia. 



These organs commence only in the XlVth segment (in the worm with sexual organs) ; 

 the whole organ is furnished with the large vesicular cells so commonly found attached 

 to the nephridia of the lower Oligochseta. The funnel opens into the segment in front of 

 that in which the organ lies; it is small, and is placed to the side of the nerve cord. 



§ Alimentary Tract. 



As no known genus of the aquatic Oligochseta possesses a gizzard,* it is almost 

 unnecessary to state that Phreodrilus, which would certainly have been included by 

 Claparede in his Oligochceta Limicolce, has no trace of such a structure. The alimentary 

 canal of Phreodrilus has in other respects the usual simple structure of the lower 

 Oligochseta. It is also, as in the Naidomorpha and Enchytrseidse, ciliated throughout, with 

 the exception only of the buccal cavity. The cilia of the pharynx and oesophagus are 

 shorter than those of the intestine, but not less obvious. The buccal cavity is dis- 

 tinguished by the short columnar cells by which it is lined. It is abruptly marked off 

 from the pharynx, particularly on the dorsal side ; the obvious demarcation between the 

 two structures is not, however, due to a sudden change in the character of the cells, but 

 to their very rapid increase in length ; the dorsal wall of the pharynx is lined by very 

 tall cells, which in the space of three or four cells, change their character to the 

 comparatively flattened epithelium of the buccal cavity. The posterior limits of the 

 pharynx are not at all clearly marked ; the epithelium very gradually decreases in 

 height, and it is impossible to fix upon any point which might be termed the junction 

 of the pharynx with the oesophagus. The calibre of the intestine is greater than 

 that of the oesophagus, and its walls are in the same way highly vascular. The 

 transition between oesophagus and intestine is not very abrupt ; the intestine seems 

 to commence in segment XIII. 



§ Vascular System. 



The vascular system in these smaller Annelids is most conveniently studied by 

 examining the living worm. As, however, I am not ever likely to have an oppor- 



* The so-called gizzard of the Naidomorpha seems to be hardly comparable to the gizzard of Earthworms. 



