180 «• «öTO. 



observed in Monocotijle and Trisiomwn those twisting movements 

 mentioned by H as well and Monti cell i. These worms, namely, 

 are capable of moving their bodies in lateral directions while keeping 

 the posterior sucker attached to a fixed substratum. This is due to 

 the crossing of the muscular fibres that enter the sucker from the 

 body and form the irregular radial fibres of the sucker already describ- 

 ed — those coming from the right side of the body going to the left 

 side of the sucker and those from the left going to the right. In this 

 connection it may be mentioned that in many specimens of T. siiiua- 

 tum which were killed with hot sublimate or heat alone, the posterior 

 suckers were seen to have l^een more or less rotated from their normal 

 position — a fact due to the unequal contractions of the irregular radial 

 fibres of the suckers. 



In all the three species above mentioned the anterior suckers 

 are chiefly used for attaching the anterior end of the body in 

 locomotion. In Monocotyh indeed there is, properly speaking, no 

 anterior sucker ; but the special development of the dorso-ventral 

 fibres already described serves in its stead. In Microcof ijle the 

 anterior end is seen, when it is being attached to a hard substratum 

 such as a glass slide, to become much broadened out. This seems 

 to be brought about by a partial evagination of the mouth-cavity, 

 by which the suckers are brought in direct contact with the 

 external object. In Tristomuni, on the other hand, the mouth, i.e., in 

 this case the anterior end of the pharynx, was often seen to be not in 

 close contact wdth the substratum, while the suckers were closely 

 applied to it. 



Food — The majority of the species described in this paper live 

 on the slime of the host ; but some are also able to extract its blood. 

 For instance, I have observed many specimens of Tristomum .'iinuatum 

 whose alimentary canal was gorged with bLjod, and they in conse- 



