ON DREPANIDIUM RANARUM. 59 



From these facts it is sufficiently evident that the Sporozoa 

 are einiuently C(?/^-parasites, that the falciform motile young 

 which escape from their spores penetrate the cells of the hosts in 

 which these animals are parasitic, and that whilst the smaller 

 forms (Coccidia) often attain the reproductive phase and form 

 their spores whilst still enclosed in a cell of their host's tissues, 

 the larger forms very generally are attached or implanted, for a 

 certain time, by one end of their bodies in the cell out of which 

 they have emerged, as necessitated by their vast increase of bulk, 

 la other cases (Gregariues velues and egg-parasites) even the larger 

 forms of Sporozoa may remain for a great part of their lives — 

 even up to the formation of spores — as intra-cellular parasites. 



Two prominent features in the history of the Sporozoa thus 

 sketched are exhibited by Drepanidnim ranariim, and appear to 

 me to justify us in associating this form with the Sporozoa, whilst 

 at the same time the " wonder ^' and '' astonishment '•' which the 

 parasite of the Frog's blood has excited, when looked at from the 

 point of view of experimental physiology alone, are definitely put 

 to rest by the association. 



The two features in question are the sickle-shape of the Dre- 

 panidium corresponding with that of the falciform corpuscles of 

 Coccidium and Monocystis, and the cell-parasitism common to 

 Urepa7iidium and the young of Sporozoa. 



The agreement of the form of Drepanidium with that of the 

 falciform corpuscles of Sporozoa is sufficiently obvious upon com- 

 parison of figs. 1 and 4 with fig. 2 c, d. The agreement, however, 

 extends beyond mere superficial form. The size of JDrepani- 

 d'mni and of the ialciform corpuscles of Sporozoa is about the same; 

 the movements of those forms among the latter which have been 

 observed to move, agree with those of the former (see especially 

 Eimer as to the active movements of the falciform young of the 

 Coccidium of the Mouse). Further, although a nucleus has 

 been observed in the falciform corpuscles of some Sporozoa, e.g. 

 of Monocystis lumljrici ; yet according to the accounts of careful 

 observers, no nucleus is to be detected in some of these falciform 

 corpuscles connected with the life-history of other species of 

 Sporozoa. Thus, in the falciform corpuscles of the Coccidium of 

 the House-mouse studied by Eimer, no nucleus has been 

 detected, and I failed to observe one in the falciform corpuscles 

 of Monocystis thalassema. 



Undoubtedly, in assimilating Brepanidium ranarum to known 

 forms of Sporozoa, it is to Elmer's parasite of the House-mouse 

 that we should be inclined to point as presenting probably the 

 nearest relationship. 



I think it, however, importaut to draw attention to the close 

 resemblance between the Drepanidium of Frog's blood and the 



