LIFE-CYCLE OF " CYSTOBJA " lEUEGULAEIS (mINCH.). 73 



regarded as more closely representing the ancestral Gregarine 

 than the Polycystids. One primitive character which has 

 been preserved, however, is the unseptate condition of the 

 body. 



Origin of association. — With regard to its sexual 

 reproduction^ our ancestral Gregarine, doubtless, greatly 

 resembled at first the parasitic Flagellate from which it 

 was derived, numerous gametes being developed inside a 

 membrane (probably little more than the unused parental 

 residue), and sexuality being by this time mai-ked ; at any 

 rate, we may assume that the male elements were smaller 

 and more active than the females. It was at this stage that 

 association made its first appearance, and to this adaptation 

 one cannot doubt that the highly successful evolution of the 

 order is chiefly due. Association, to conimence with, would 

 be quite accidental and indiscriminate, at first only occurring 

 to any purpose between individuals which were dividing up 

 to form gametes, when we may suppose them mutually 

 capable of exerting an attractive or cytotactic influence. 

 Such a coming and reiiiainiug together would obviously 

 allow of a far greater percentage of the gametes copulating 

 than if the male elements had to wander about trying to 

 find the female ones. In other words, successful reproduc- 

 tion — ample provision for which is especially necessary in a 

 parasite — would be much facilitated and increased. The 

 advantage thus gained would lead to the development of 

 this beneficial modification, and reciprocal attraction would 

 not only be strengthened, but would tend to be manifested 

 earlier, before the gametes were formed. In this way we 

 get the cytotactic (chemiotactic ?) influence thrown back to, 

 and becoming apparent in, the parent individuals — that is, 

 the adult Gregarines themselves. It is but a slight step in 

 advance to suppose that this gradually led to the formation 

 of the gametes being regulated by, and dependent on, the 



1 Asexual reproduction, it may be nienlioned, lias become completely lost 

 in most Greearines. 



