OBSERVATIONS ON THE GREGAEINBS OP HOLOTHURIANS. 281 



My own acquaintance with these interesting parasites began 

 in the year 1889, when as a student in the Oxford Laboratory 

 I found a specimen of Holothuria tubulosa, from Naples, 

 supplied for dissection, with its body-cavity filled with cysts, 

 some containing sporoblasts, others ripe psorosperms or 

 spores. Having investigated these cysts and their contents, 

 and written a short description of them, I forwarded the 

 description with some material to Professor Biitschli, of Hei- 

 delberg, whose pupil I had had the honour and pleasure to be 

 for a short time during the previous summer. Professor 

 Biitschli with characteristic kindness examined the material, 

 and in a letter accompanied by a sketch pointed out to me 

 that I had overlooked the most important points, viz. the for- 

 mation of the sporozoites within the spore. I determined, 

 therefore, before publishing anything, to examine fresh mate- 

 rial, which I was fortunately able to do both at Plymouth in 

 the summer of 1890, when as the occupant of a British Asso- 

 ciation table I studied the Gregarines of Holothuria nigra, 

 and at Naples, during my occupation of the Oxford table 

 there in 1891-2. The results of my investigations on the two 

 closely allied gregarines found in these Holothurians are far 

 from complete, but it seemed to me better to publish them in 

 their present crude form than to wait, perhaps, some years 

 before I can complete them. Like Kolliker, I would simply 

 recommend these interesting forms to later observers, who 

 will, I hope, fill up the gaps in the following description. 



I shall begin with the description of the Gregarine of Holo- 

 thuria nigra, in which my series of stages is most complete. 

 This Holothurian occurs commonly at Plymouth, and can be 

 obtained in numbers. The dissection of the animal is not 

 without its difficulties, both on account of the large number of 

 Cuvierian organs it emits, and by reason of the force with 

 which its powerful body muscles contract on the least stimu- 

 lation, thereby much impeding the examination of the fresh 

 contents of the body-cavity. In the majority of the speci- 

 mens of Holothuria nigra observed by me the blood-vessels 

 could be seen to bear little stalked vesicles, which on exami- 



