20 WRIGHT AND MACALLUM. [Vol. I. 



the nucleus occurs in greater quantity. A membrane is present 

 to each cell, but it is sometimes detectable with difficulty. 



Scattered amongst the connective tissue cells, and chiefly 

 near the posterior termination of the intestine, are numbers of 

 cells, which measure 10-12 yt in diameter, and whose signifi- 

 cance cannot be determined at present. (Fig. 10,/.) They 

 are unlike the ordinary connective tissue elements, appearing 

 polyhedral, sometimes fusiform, and when they are found in 

 groups the adjoining faces of neighboring cells are in contact. 

 The nucleus in each is somewhat shrunken, and contains 

 one or two chromatin nucleoli. The cell protoplasm is clear, 

 homogeneous, and unstainable. From their position these 

 structures appeared to be muscular in their nature ; but a con- 

 nection with muscular fibres, or with fibres of any sort, was not 

 demonstrated. They may possibly represent the structures 

 which have been interpreted as cutaneous glands in other Tre- 

 matodes, but they apparently have no glandular character. 



These comprise all the forms of connective tissue cells, but 

 there are mingled with them the central bodies of the muscular 

 fibres, as described above, and large, clear cells throughout the 

 body and muscular pharynx, which are fully described under 

 the Excretory System below. 



The Excretory System. 



The course and manner of opening of the excretory vessels 

 have not been accurately studied in many of the monogenetic 

 Trematodes; but Sphyranura agrees with Polystomum, as de- 

 scribed by Zeller, in the possession of two anterior contractile 

 bladders, each of which opens by a dorsal pore towards its 

 anterior end. Onchocotyle, which, as we have seen, is gener- 

 ally associated with Polystomum under the sub-family Poly- 

 stomidae, has its contractile bladders in the bifid appendage of 

 the caudal lamina ; whereas the Tristomese which have been ex- 

 amined have the bladders anteriorly, as in Sphyranura. 



The dorsal pores of the pulsating bladders escaped us in pre- 

 served specimens, but they are readily seen in the fresh worm 

 when it is lying on its ventral surface. The transparency of the 

 tissues overlying the bladders offers a favorable opportunity 

 for observing, in their natural condition, the large ganglion cells 

 which are applied to the wall of the bladders, and, presumably, 



