6 H. M. WOODCOCK. 



the same bulk, the chief differences between them being in 

 respect of form and movement. 



In other words, sexual differentiation in the latter genus is 

 less marked. There can be little doubt, it seems to me, that 

 this condition represents an early step in the direction of 

 isoganiy. I hold that isogamy in the Gregarines is secondary, 

 and derived from auisogamy, being, in fact, closely correlated 

 witli the phenomenon of association ; this subject, hoAvever, 

 Avill be fully discussed later (see p. 73, et, seq.). 



(2) Methods. 



(a) Examination. — In examining both Holothuria and 

 Cucumaria for the parasites, the dissection was rendered 

 much easier by leaving them for some time previously in 

 a jar of sea-water, to which a few crystals of menthol had 

 been added. This stupefied the animals, and always in an 

 expanded condition. If they were taken out after a few 

 hours, before death had occurred, the Gregarines were in no 

 way affected, as they do not inhabit the gut. By this precau- 

 tion I avoided the disagreeable extrusion of the Cuvieriau 

 organs and the violent contractions of the body which other- 

 wise take place. 



On opening a Holothurian it is easy to ascertain, by 

 scrutinising the vascular network and blood-vessels gener- 

 ally, whether any parasites are present. They show up dis- 

 tinctly either as little white, oval spots if in the lumen, or as 

 spherical cysts if attached to the wall. In the former case 

 it is a very delicate matter to obtain the Gregarines free 

 without injuring them. I followed Minchin's procedure, 

 snipping the vessel close to the parasite on either side and, 

 by gently pressing the wall, causing the Gregarine to pass 

 out. Sometimes, however careful I was, when at length I 

 got the Cystobia safely on a slide, it would be distorted 

 and irregular in shape, although touched as little as possible 

 during the manipulation (for tlie reason, see p. 25). 



in the case of C minchinii in the Cucuniariio the 



