ZooL— Vol. II.] RISEN— OLIGOCHMTA. 131 



while the glandular layer increases. Hence the muscular 

 duct is composed of two sections, each section occupying 

 two somites. The part which is most glandular contains 

 two different kinds of alternating glandular cells. The 

 narrow cells are similar to those in the muscular prostates ; 

 the larger ones resemble those in the glandular part. In 

 the glandular part there is only a single row of glandular 

 cells, commencing with somite XXI. 



Lymphocytes. — (figs. 114-116.) The free coelomic cells 

 of this variety are of more than usual interest, one kind 

 being a most extraordinary structure. The following kinds 

 are distinguished. 



Nematocytes. — This name is proposed for a highly spe- 

 cialized lymphocyte found in great numbers in the lymphatic 

 fluid of this species. These cells are erythrophile, staining 

 intensely with eosin and fuchsin. The whole cytoplasm is 

 jiliform and takes the shape of a single, continuous, narrow 

 strand wound regtilarly like a coil of rope. Seen from the 

 flat side these cells are irregularly rounded. The winding 

 of the strand begins at one end or surface and continues 

 regularly, ending at the other surface-end or pole. Where 

 the cells had been torn, it was frequently found that a por- 

 tion of the nematocyte had been carried some distance 

 away without any break in the cytoplasmic thread, part of 

 which could be seen more or less uncoiled, connecting the 

 two portions of the cell. In many instances the beginning 

 and the end of the thread could be clearly seen. The first 

 coils nearest the pole are narrow, but they gradually widen 

 until they reach their greatest diameter, which is that of the 

 cell ; then again they gradually diminish and finally end as 

 they began. The thread does not contain any microsomes 

 of unequal size, but there is some differentiation, so that 

 alternating divisions stain darker. These alternate divisions 

 appear to be of the same size, but are so minute as to be 

 but indistinctly seen. In optical section the thread is round. 

 The nematocyte is not covered by an exterior membrane 

 (cytotheca), but the boundary of the cell consists alwa5'^s of 

 the margins of the cytoplasmic rope. There is no cytoplasm 



