OBSERVATIONS ON THE GREGARINES OF HOLOTHURIANS. 285 



be chromatin^ and the clear unstained vacuoles achromatin ; 

 but it would be unsafe to identify the two constituent parts 

 of the nucleolus as such simply from their reaction to stains. 

 With all due caution, however, a comparison may be made with^ 

 for instance, the results obtained by Pictet (8) in studying the 

 spermatogenesis of Echinoids, where the achromatic portion 

 of the nucleus of the spermatocyte separates out to form a 

 number of vacuoles or " cytomicrosomes,^^ which fuse together 

 to form the single " Nebeukern.'^ I am not aware that a nucleus 

 of similar structure has as yet been described, though it is an 

 old observation that the nucleoli of Gregarines often contain 

 vacuoles (see Butschli, 6, p. 525). Wolters (9), in his 

 valuable studies on the conjugation and spore formation of 

 Gregarines, describes the nucleolusofClepsidrinablatt arum 

 as containing ''more strongly stained spherules of varying size 

 and shape ^' (p. 118): the nucleolus of Monocystis agilis is 

 similarly described (p. 106). Schneider (' Tablettes zoo- 

 logiques,' i, pi. vi, fig. 9) figures the nucleus ofPileocephalus 

 chinen sis, containing numerous spherical nucleoli, some dark, 

 others light. The vacuolar structure of the nucleolus in the 

 Gregarine seems to me to support strongly Professor Biitschli's 

 theory of the frothy structure of protoplasm. 



The greater number of Holothurians examined had, as has 

 been said above, stalked vesicles attached to the blood-vessels 

 which contained cysts. Some of these cysts I teased up and 

 examined the isolated spores, while others I cut into sections. 

 As it turned out I was not particularly lucky in my selection, 

 for the only cysts which were found to contain perfectly 

 mature spores were the very ones I had selected for sections ; 

 while among those teased up one was found to contain, besides 

 sporoblasts, large nucleated masses of protoplasm, the relation 

 of which to the sporoblasts it was of course impossible to 

 ascertain by this method. 



Fig. 10 represents one of these cysts attached to the blood- 

 vessels, and fig. 9 shows another, which had an exceptionally 

 long stalk ; 9 a represents a portion of the edge of the same 

 cyst in optical section. 



