I 26 W. C. CURTIS. 



line of some ot the general problems involved in Cestode para- 

 sitism and development in addition to the possible opportunity 

 for fixing the life history of this particular form. With this iir 

 mind I have been collecting all the data bearing upon the life his- 

 tory and during the summer of 1902 I made the first of a series 

 of experiments in infection which I hope to continue and which 

 may lead to more precise knowledge concerning the identity of 

 the larva found in the squeteague. 



I wish in this paper to describe the important features in the 

 structure of the motile proglottids, its egg-laying and other activ- 

 ities, to give some observations on the larva from the squeteague 

 and to discuss the view point which my study of the development 

 in this and other Cestodes has suggested to me. 



THE MOTILE PROGLOTTIDS. 



When an incision is made in the spiral valve of an infected 

 " sand shark " the Cestode is frequently found in such abundance 

 that, as the elongated bodies and the motile proglottids writhe 

 about in the chyle, one often wonders how there can be enough 

 nourishment left for the host. I can confirm Linton's record, of 

 " sand sharks " taken at different times, that in the great majority 

 of individuals there are literally hundreds of this parasite in the 

 spiral-valve to the exclusion of all others. When the parasites 

 are examined in sea-water the alternate protrusion and retraction 

 of the bothria, as described by Linton, can be observed for hours. 

 When a scolex is compressed on a slide the flame cells of the 

 water vascular system can be observed for a considerable time 

 before they succumb to the abnormal conditions. 



The ripe proglottids which can be pulled from the long strobilae 

 or found loose in the intestine are very active and constantly 

 changing their shape. A typical outline in a partially extended 

 condition is represented in Fig. I, and the fully elongated condi- 

 tion is represented on a smaller scale in Fig. 2. At the anterior 

 tip I have found in preserved specimens minute projections which 

 have the appearance of cilia (<r), but which will probably prove 

 upon examination in the living specimen to be minute spikes sim- 

 ilar to the larger ones on the penis (/>). 



The four ear-like flaps at the posterior end which give the 



