A NEW SPOROZOON IN AMPHIOXUS. 313 



treraities of the epithelial cells, are usually situated in cavities 

 at the proximal ends of the cells. Sometimes a single para- 

 site is found in an isolated position in the digestive epithelium ; 

 but most frequently they occur in groups, and seem to exert 

 some irritating influence over the epithelial cells, causing 

 these to curve round to form the curious cup-like structures 

 drawn in figs. 1 and 4. Not unfrequently the distal extremi- 

 ties of the cells containing parasites are broken away (figs. 7 

 and 8) ; but this by no means invariably occurs, and may be 

 due to the preparation of the sections. 



The extremity of the parasite nearest the free edge of the 

 cell is in close proximity to the cell nucleus (M in figs. 7, 8, 

 and 9). The nucleus of the infected cell, moreover, difi'ers 

 considerably in form from that of the normal epithelial cell 

 (figs. 7 and 8, M' ). It seems probable that the parasite, by 

 pushing against the nucleus, had altered its form until, as in 

 figs. 7, 8, and 9, a and 6, it has the appearance of a granular 

 cap to the parasite. 



I have not seen stages showing the alteration of the nucleus ; 

 but Schneider, in his 'Tablettes Zoologiques,' figures such a 

 change brought about by the pressure of a growing Sporozoon 

 (vol. i, pi. ix and xxix). In the form described by Schneider 

 the nucleus is situated at the proximal end of the cell, the 

 parasite being more distal in position, whilst in the form now 

 described the nucleus is nearer the free end of the cell than the 

 parasite. 



As for the distribution of these parasites in Amphioxus, 

 they occur all round the intestinal epithelium, but are limited 

 to the posterior region of the gut from the atriopore to the 

 anus. In this post-atrioporal region they may be extremely 

 numerous, the epithelium, as in fig. 3, being crammed with 

 them. 



The epithelium of the hepatic caecum is so similar to that of 

 the intestine that I had every expectation of finding these cells 

 also infected. 



Although, however, I have sought with the utmost care, 

 both in my own sections and in some excellent series, for the 



