290 E. A. MINCHIN. 



is now four or five times as long as broad, and the tail longer 

 still. Both nucleus and tail are often slightly flexed, especially 

 when the sporozoite lies close along the side of the spore. 

 Both in this stage and the last the nucleus does not stain 

 evenly, but more darkly in some parts than others. 



There remains now only to be considered the Gregarine 

 represented in fig. 2. This is seen to be separated into two 

 halves by a septum, in each of which are four nuclei. I was 

 at first inclined to consider the septum as produced by the 

 fusion of two animals, but am now more inclined to consider, 

 for reasons which will be set forth below, the ordinary bi- 

 nucleated adult form as itself produced by the fusion in early 

 life of two separate individuals. In this case it is more pro- 

 bable that the form shown in fig. 2 is the commencement of 

 segmentation in an animal that is about to encyst and form 

 sporoblasts, and that the septum separates what we may term 

 the first two sporoblastomeres. No enveloping cyst-mem- 

 brane was to be seen in this specimen, but that might have 

 been torn oflFin removing it from the blood-vessel. 



It would be extremely interesting to follow the first stages 

 of segmentation in the encystment of this form. By the 

 analogy of what Wolters (9) has observed in Monocystis 

 magna and agilis it is to be supposed each nucleus would 

 give ofi" a polar body. Only by the observation of this process 

 could the meaning of the vacuolar structure of the nucleolus 

 be properly understood. After formation of the cyst the 

 enclosed animal segments into sporoblasts, which are formed, 

 in a method yet to be described, first at the periphery. While 

 this process is going on the wall of the blood-vessel becomes 

 evaginated to form the stalked vesicle containing the cyst. 

 What causes this evagination it is difficult to understand. It 

 must be due to active growth on the part of the tissues of the 

 host, brought on, however, in some way by the parasite. In 

 Holothuria tubulosa we shall see that the evagination 

 takes place at an earlier stage in the life of the Gregarine 

 than in H. nigra. 



To recapitulate, the following arc the characters, as far as 



