Anatomîcal structure of Aspidogaster conchîcola. 531 



for me since to compare a great number of cases in order to find if 

 the exceptional direction of motion often occurs. Until that is done 

 we should perhaps not build too much on conclusions as to their 

 meaning, but of this we can be certain viz. that they are of im- 

 portance. In the first place we can not avoid the conclusion that 

 the cilia are intended for the spermatozoa, for in a tube whose walls 

 constrict round its contents the cilia can have little effect in moving 

 along heavy primitive eggs or yolk cells. Besides it is the destiny 

 of both of these, under normal conditions, to move in the opposite 

 direction. Of the three elements that may be found in this region, 

 the normal direction of transport of the spermatozoa alone corresponds 

 with the action of the cilia. However, as the cilia begin at the point 

 where yolk enters the oviduct, it is suggestive that they might stand 

 in some relation to it, which only begins to become intelligible when 

 we associate with the two the spermatozoa as a third, most interested 

 party. Why sperm should require the assistance of cilia in this short 

 space after coming through all the windings of the oviduct is again 

 a question. But I have already indicated that the transfer of sperm 

 probably takes place to the greatest extent in the young animal when 

 there are no eggs moving in the opposite direction. The spermatozoa 

 are held in readiness in great numbers in the receptaculum seminis 

 uterinum, only passing over through the ootype singly, by their own 

 efforts. In the ciliated space, between yolk duct and Laurer's canal, 

 there may be primitive eggs coming down as the spermatozoa go up. 

 The thick-walled and hence somewhat strong and constricted ciliated 

 portion may be stopped up with primitive eggs, or what more frequently 

 happens with yolk cells which, backed up by great pressure from 

 behind, find least resistance in this direction. In such cases the action 

 of the cilia may be of great use in freeing the mass and brushing 

 away fastened sperm cells and directing them towards the tuba. 

 Movement of the eggs and yolk outwards can only be produced by 

 contractions in the walls of the oviduct. Here, too, is doubtless the 

 proper function of the muscular- chambered tuba. The eggs pass 

 slowly out, one by one, from one chamber to another, meeting with 

 sperm cells on their way, and are prevented from a backward motion 

 by the musculature of the chambers. Strong contractions of the 

 walls may clear all the ova, yolk, and sperm away, yet the latter are 

 least likely to be affected by contractions. Under such conditions, 

 too, any of these elements may be pressed into the Laurer's canal. 

 The continuation of cilia from both tuba and ciliated portion of the 



