150 



Microcotyle^ Gyrodactylus, Dactylogyrus^ Pseudocotyle and Tristomum: 

 it may, in fact, be said, as pointed out by B r a u n , that any other mode 

 of opening is to be looked upon as the exception among the Monoge- 

 naea. But in several other respects the excretory system of Temnoce- 

 phala presents features which have not been detected , if they occur, 

 in other Platyelminthes. 



Each of the two excretory openings leads into a thick-walled, con- 

 tractile terminal sac of a pyriform shape with a curved apex. A 

 layer of muscular fibres encloses the sac , but the greater part of the 

 thickness of its wall is composed of a thick layer of finely fibrillated 

 protoplasm. In this there are no nuclei as far as the dilated body of the 

 sac is concerned; but in the wall of the curved narrow portion, where 

 it merges into the main canal there are two large nuclei at some little 

 distance from one another : These two nuclei were formerly supposed 

 by me to be the nuclei of nerve-cells closely applied to the terminal 

 vesicle ; but a careful re-examination of series of sections has shewn 

 this to be an error : the nuclei are of exactly the same character as the 

 nuclei of the excretory cells to be presently described ^. The terminal 

 sac is in reality a perforated cell with its nucleus situated in its narrower 

 posterior portion. The second nucleus is the nucleus of a narrow 

 perforated cell the lumen of which is the cavity of the posterior part 

 of the terminal sac and its contiuation into the principal vessel. At 

 various other points in the course of the main vessels there are nuclei 

 of similar character; but these are very few, there being not more than 

 twenty of these nuclei altogether. 



The main excretory canals are thus intracellular, as well as the 

 terminal vesicles — the walls of the entire system, so far as the larger 

 trunks are concerned , being composed of a very limited, number of 

 very greatly produced and sometimes branched cells. 



These main branches give origin to a system of canalicules or 

 capillaries of small calibre and thin walls , and »Wimperflammen« are 

 to be detected at various parts of the body , though always very few 

 in number : but the precise relation between these has not been deter- 

 mined. 



From each main trunk, not far from its origin, there is given off 

 a branch which has a very remarkable destination. It quickly divides 

 to form a number of vessels which enter the wall of the terminal 

 vesicle and ramify through its substance, giving rise to a complicated 



3 Wright and Macallum in their account of Sphyranm-a Osleri (Journal of 

 Morphology. Vol. I. p. 20) describe ganglioncells as applied to the excretory vesicles 

 in that Trematode. It appears to me not improbable that they have here fallen into 

 the same error as myself. 



