REPRODUCTION OF EHIZOPODA. — GREGARINIDA. 447 



Vesicle ; for each segment very early shows itself to be provided 

 with its own (Fig. 233, B, o, o), and the two vesicles are commonly 

 removed to a considerable distance from one another. The seg- 

 ments thus divided are not always equal, and sometimes their dif- 

 ference in size is very considerable. — On the other hand, a junction 

 of two individuals has been seen to take place in Actinophrys, 

 which has been supposed to correspond to the ' conjugation ' of 

 Protophytes. It is very doubtful, however, whether this junction 

 really involves a complete fusion of the substance of the bodies 

 which take part in it ; and there is not sufficient evidence that 

 it has any relation to the act of Reproduction. Certain it is that 

 such a junction or ' zygosis ' may occur, not between two only, but 

 between several individuals at once, their number being recognized 

 by that of their contractile vesicles ; and that, after remaining 

 thus coherent for several hours, they may separate again without 

 having undergone any discoverable change. — It appears from the 

 observations of Mr. H. J. Carter,* that a distinction of Sexes 

 exists among Amcebina and Actinopkryna ; bodies resembling 

 spermatozoa being developed from the nucleus in certain indivi- 

 duals, whilst in others ova seems to be dispersed through the 

 general substance of the body. And these observations derive an 

 increased significance from the discoveries which have been lately 

 made by M. Balbiani respecting the Sexual propagation of Infusoria 

 (§ 347). But Mr. Carter has not yet succeeded either in tracing 

 any relation between the ' zygosis ' just mentioned as occurring 

 between two or more individuals, and the fertilization of the ova 

 by the spermatozoids ; or in ascertaining with certainty whether 

 the product of each ovum is a single Rhizopod, or an aggregation 

 of independent Rhizopods ; and these problems have still to be 

 worked out.f 



335. Gregarinida. — A very curious animal parasite is often to 

 be met with in the intestinal canal of Insects, Centipedes, &c, and 

 sometimes in that of higher animals, the simplicity of whose struc- 

 ture requires that it should be ranked among the Protozoa. It 

 is not yet certain, however, that we know the entire life-history 

 of this parasite, the Grer/arina; and it may possibly be only a 

 phase in the existence of some higher kind of Entozoon. Each 

 individual (Fig. 236, a) essentially consists of a single cell, usually 

 more or less ovate in form, and sometimes considerably elongated ; 

 a sort of beak or proboscis frequently projects from one extremity ; 

 and in some instances this is furnished with a circular row of 

 hooklets, closely resembling that which is seen on the head of 

 Tsenia. There is here a much more complete differentiation 



* 'Notes on the Freshwater Infusoria in the Island of Bombay,' in 

 "Annals of Nat. Hist.," 2nd Ser., Vol. xviii. (1856), pp. 223-233. 



t A summary of the present state of our knowledge upon the Repro- 

 duction of the Rhizopoda is given in the Author's " Introduction to the 

 Study of the Foraminifera," published by the Ray Society, 1861. 



