MUSEUM OF COMPARATIVE ZOOLOGY 5 



and when protruded reach the exterior through a single orifice, but they 

 open into the intestinal cavity separately. One of these pharynges, 

 like the single pharynx of other Triclads, joins the intestine at the 

 junction of its main trunks ; the others are connected with the inferior 

 median surface of the lateral trunks (Plate II. Fig. 20). The odd 

 median pharynx is largest, and therefore most prominent of all. The 

 others, which arise from the intestine farther back, are successively 

 shorter, as well as narrower, the more remote they are from the median 

 proboscis. The attachment of the smallest ones is about as far from 

 the posterior end of the animal as the attachment of the chief one is 

 from its anterior end, so that the chamber which they all occupy em- 

 braces the middle half of the body. Although there are about as many 

 pharynges attached to one of the lateral trunks of the intestine as to 

 the other, they are not arranged in pairs, nor have their positions any 

 definite relation to the side branches of the intestine which open into the 

 lateral trunks. The pharynges are rather less numerous than the side 

 branches ; they sometimes arise opposite to a branch, sometimes oppo- 

 site to a space midway between two branches, or at other intermediate 

 points. The foremost of the lateral pharynges is often considerably 

 in advance of the corresponding proboscis of the opposite side of the 

 body (Fig. 20). Leidy ('48, p. 249) has well described the appearance 

 and action of the pharynges in the living animal. He says : " They 

 are considerably longer, but narrower, than in P. lactea, and when not 

 in use are packed together within the animal, so that, when the latter 

 is placed beneath the microscope and slightly compressed, they will 

 be seen pressing upon one another in such a manner that, if one 

 changes its position, it will be instantly occupied by another. Those 

 which are formed last are smallest, but they soon gain their full size. 

 If one of these animals be punctured or cut, one or more of the pro- 

 boscides will be instantly protruded as if they existed under pressure, 

 and will move about in all directions, appearing as if entirely without 

 the control of the animal ; or if one of the animals be crushed between 

 two slips of glass so that the proboscides will be torn from their attach- 

 ment, they move about involuntarily, always in a line forwards or towards 

 the mouth. ... In this progressive course they constantly contract 

 and dilate ; the mouth opens, and any matter in its vicinity rushes in, 

 when it is closed and the matter passes onwards, and by the alternate 

 contraction and dilatation of different parts of the same tube it is 

 thrown backwards and forwards several times, and finally violently 

 expelled at the torn extremity. When they have escaped from the 



