OBSERVATIONS ON THE GKEGAlilNES OF HOLOTHURIANS. 299 



from one another. It seems to me not improbable that this 

 represents young specimens of a Gregariue allied to those 

 described in this paper. Nevertheless I do not consider it as 

 by any means proved that these Gregarines are really each a 

 pair of individuals, and have therefore not included this cha- 

 racter in the diagnosis of the species. 



To discuss the affinities of these forms it will be convenient 

 to begin by tabulating the characters in which the two species 

 agree with, and differ from, one another respectively. 



A. They agree with one another — 



(1) In the general structure of their cuticle, protoplasm, and 

 nucleus. 



(2) In the possession of two nuclei. 



(3) In using up all the body protoplasm to form sporoblasts, 

 from each of which a spore develops. 



(4) In the shape of the spore, the arrangement of its cuticle, 

 and the possession of a funnel at the narrow end. 



(5) In forming eight sporozoites. 



(6) In the general structure of the sporozoites, which have 

 a nucleus at the anterior end, to which is attached a flame- 

 like tail posteriorly. 



(7) In the fact that both pass the chief period of their exist- 

 ence in the blood-vessels of Holothurians. 



B. Leaving out mere details, they differ in the following 

 points : 



(1) Inform; G. irregularis appears to keep its irregular 

 shape up to the time of encystment, while in G. holothurise 

 it is only present in the young stage. 



(2) In the presence of a caudal process to the spore in G. 

 holothuriae, which is entirely wanting in G. irregularis. 



(3) Perhaps in the form of the sporozoites, especially in its 

 nucleus. 



(4) G. holothurise is contained in stalked vesicles formed 

 by evagination of the blood-vessel long before encystment, and 

 breaks loose into the body-cavity to sporulate, while G. irre- 

 gularis appears not to evaginate the wall of the blood-vessel 

 until ready to encyst, and to sporulate in the vesicle. 



