No. I.] SPHYRANURA OSLERF. 2/ 



The cell-body and the nucleus rarely take any stain at all in 

 chrom-osmio-acetic preparations, with the exception of one or 

 more nucleoli, which may be present. The limits of the cell 

 are often quite indefinite, and this, with the somewhat large 

 trabeculse, makes them resemble the figures which Looss has 

 given of them. Where the cell limits are clear and distinct the 

 cytological structure is usually obscure for some reason, and in 

 these cases their complete independence of the muscular ele- 

 ments lying around them is definite and decisive. (Fig. 6.) 

 They sometimes have a concavo-convex nucleus, which may often 

 be shrunken, while the cell in the fresh condition has in several 

 cases been observed to have a process like that possessed by 

 the renal cells. These cells in Sphyranura are, doubtless, the 

 homologues of the cells described by Looss as found in the 

 muscular pharynx of Distomum trigonocephalum, and the ques- 

 tion naturally arises whether the cells, as Looss represents them, 

 are not artificially affected by the reagents he has used to de- 

 monstrate them. Treatment with nitric acid, such as he used, 

 however clearly it may bring out the coarser details of these 

 cells, cannot certainly be depended on to preserve with any 

 degree of accuracy the finer cell-structure, and we must, there- 

 fore, doubt if the coarse reticulum which he finds in it and the 

 passage of muscular fibres through the meshes of this reticulum 

 represent a natural condition. 



The nature of these cells has been variously interpreted. 

 According to the extreme and very absurd view of Villot ^ they 

 are not really cells, but transections of vascular dilatations of 

 the excretory system, which by an optical illusion have come 

 to be considered as cells. All the other observers, with the 

 exception of Looss, Fischer, and Leuckart, who have referred to 

 these structures, regard them as ganglion-cells. Lang^ described 

 in Tristominn moles the connection of these structures with the 

 ganglion cells. Leuckart regards them as glandular; Fischer is 

 doubtful of their nature ; while Looss considers them to belong 

 to connective tissue. 



In order to determine as carefully as possible the nature of 

 these cells we compared them with the cells found in the oral 

 and caudal suckers of Amphistotnum subclavtum. Speci- 



' Ann. de Zool., 1878, p. 14. 



*Mitt. Zool. Stat.,Neapel. II., p. 44. 



