64 U. M. WOODCOCK. 



biuuclear Gregariiie. Fig. 3 represents the least iutimately 

 joined couple that I have observed. lu this case associatiou 

 had probably taken place but a short time previously. With 

 growth, however, the " double " nature of the parasite (as 

 indicated by the V-shaped consti-iction) would, doubtless, 

 have become less and less obvious, until the typical adult 

 condition was reached (figs. 1, 2). On the other hand, many 

 individuals unite at the earliest opportunity and very inti- 

 mately;^ in such cases the actual cytoplasm of the two 

 associates becomes joined," and there is no indication what- 

 ever of the plane of union.^ 



In D. minchinii complete union of the two associates is 

 found in all cases (cf. figs. 9, 10, 12, 18, and 19). This 

 species, so far as the cytoplasm is concerned, is absolutely 

 indistinguishable from an ordinary Monocystid Gregarine. 

 The only clue, indeed, to the plane of junction is the 

 invariably transverse arrangement of the nuclei (see above, 

 p. 21). 



There can be no doubt that the presence or absence of a 

 partition between the two associates depends upon how soon 

 neogamy occurs. Where we find an intimate C3^top]asmic 

 union it is almost certain that the association has taken place 

 between naked sporozoites, when there would be no limiting 



' Associations belonging to this category appear to be more numerous as 

 the seasou advances. Probably such factors as temperature, change of season, 

 and tlie supply of nutriment available in the host at the time, exert an 

 influence on the parasites, and induce them to anticipate, and prepare for, 

 the ultimate phase of their existence— sporulat ion. 



^ Tiiis fusion is not to be considered coni|)arablc to the complete and homo- 

 geneous union which occurs in actual conjugation (see below, p. GS). 



' The position of Cystobia iiolothurijB with regard to this biological 

 feature is somewliat doubtful. Mingazzini (27) says that a septum divides 

 the Gregarine while it is attached to the blood-vessel, but Schneider (35) 

 only saw one in cysts which had fallen off into the body-cavity. Minchiu 

 (25), again, did not see a septum in any case. Probably the explanation of 

 these conflicting observations is that this parasite exhibits the same variation 

 in this respect that D. irregularis does. Furtlier study of the earlier 

 phases of the life-history, while the trophozoites arc still in the vessels, is 

 necessary to decide the point. 



