386 
The Schizogregarines 
Selenidiidae, while they also saw some analogy with Amoebidium. 
Inasmuch as the protozoal nature of the latter organism has now 
been refuted, while Siedleckia is undoubtedly a Protozoon, the com¬ 
parison with Amoebidium cannot stand. On the whole, it would be 
well to place Siedleckia and Schizocystis in one group, as Brasil 
(1907) has done, a course that has been followed by Leger and 
Duboscq, uniting them on account of their similarity of habitat, their 
resemblance to one another when undergoing nuclear multiplication, 
and their method of formation of daughter forms containing one or 
more nuclei. 
The multinucleate condition of the trophozoite, forming a so-called 
“ plasmodial ” stage, has led Caullery and Mesnil (1905) to discuss 
Siedleckia in their excellent paper on the Haplosporidia. Until 
something is known as to the existence or otherwise of sporogony, 
the definite systematic position of Siedleckia cannot be fixed. In the 
preparations which I have seen, a structure of the nature of an epimerite 
seems to exist, and this feature would accentuate the gregarine-like 
character of the parasite. 
(5) Family Selenidiidae. 
There is at present one well-defined genus in this family, viz. the 
genus Selenidium. This genus is, however, somewhat difficult to 
define from the point of view of a complete life-cycle. The species 
placed therein, by Labbe (1899) (under the name Polyrhabdina), are in 
some cases very doubtful members of the genus. The type species is 
Selenidium pendula Giard (1884), originally described as from the 
body cavity of Nerine sp. S. pendida possesses longitudinal myonemes. 
The habitat of this parasite as given by Giard is incorrect, for Caullery 
and Mesnil (1899) re-discovered it in the digestive tract of Nerine 
cirratulus. Selenids were undoubtedly seen earlier ( e.g . Kolliker 1845), 
but were usually considered to be Nematode embryos. 
Mingazzini (1891) described Selenid forms, since they possessed 
longitudinally disposed myonemes, under the generic names of Poly¬ 
rhabdina and Esarhabdina, according to the large or small number of 
the myonemes present. In 1892 Leger described trophic phases of 
Gregarines, which he placed in a new genus Platycystis, possessing 
myonemes longitudinally arranged, in some cases with a spiral twist. 
In 1898 Caullery and Mesnil contributed a very important paper 
on a Gregarine exhibiting a schizogonic phase in its life-cycle. The 
