OBSERVATIONS ON THE GEEGAEINES OP HOLOTHURIANS. 293 



mens floating free in the body-cavity, and could observe none 

 in those still attached to the blood-vessels. My observations 

 agree completely with Schneider, as I never could observe 

 any septum in the specimens still attached to the blood-vessel. 

 On the other hand, since sporulatiou certainly takes place in 

 the body-cavity, it is probable that the septum seen by Schnei- 

 der was that dividing the first two sporoblastomeres, as I 

 have termed them above. 



If we sum up the above somewhat conflicting evidence, the 

 following seems to me the most probable history of this para- 

 site. The adult form inhabits the blood-vessels of Hoi othuri a 

 tubulosa, probably coming there from the intestine. As it 

 grows in size it evaginates the walls of the vessels, and hangs 

 into the ccelom. When it is ripe and ready for sporulation 

 the vesicle breaks ofi" and drops into the coelom, and sporula- 

 tion then takes place. 



To return now to our specimens. Like Gregarina irregu- 

 laris, this form has a distinct cuticle singly contoured. In 

 sections it seemed to me that I could distinguish an outer zone 

 of protoplasm marked ofi" from that more internal, which I have 

 represented in fig. 23, a. The granules in the outer zone are 

 more regularly and evenly arranged than in the inner part, 

 and appear also more of a size. If this diS'erentiation, however, 

 can be compared with what is known as ectosarc and endosarc 

 in other forms is very doubtful. The nuclei are placed in a 

 clear space, relatively larger than in G. irregularis. In its 

 general characters the nucleus resembles that of G. irregu- 

 laris. It has a distinct membrane, generally somewhat 

 shrunk in preparations made with Kleinenberg's picric, but 

 retaining its even round contour after Memming's fluid. The 

 nucleus contains a large space, which often appears very 

 granular ; but I have never been able, with the highest power, 

 to see the "delicate reticulum" described by Mingazzini (5, 

 p. 315). The nucleolus has the same vacuolar structure as 

 that described above, but not quite so well marked, and there 

 is not always a vacuole specially marked out by its size.^ 



' This seems to me the proper place to notice the recent work of Feenzei, 



VOI<. XXXIV, PART III. — NEW SEE. U 



