372 THE PROTOZOA 



monly in the latter as the so-called " leucocytozoa," not to be con- 

 fused with the true leucocytozoa dealt with in the last section. 



Haemogregarines present themselves usually as more or less 

 elongated parasites of quite definite form, sausage-shaped or worm- 

 like, not amoeboid, lying within the blood-corpuscle. The middle 

 of the body is occupied by a conspicuous nucleus, and there are 

 often numerous metachromatinic grains in addition, but no melanin- 

 pigment is produced. The parasite may be liberated from the 

 corpuscle as a free vermicule, the resemblance of which to a small 

 gregarine is accentuated by its active gliding movements ; liberation 

 of the vermicules may often be seen when the blood is drawn, but 

 no " exflagellation " ever occurs, since, as will be seen when the 

 development is described, the microgametes are formed in a manner 

 totally different from that characteristic of the haemamcebae. 



In many haemogregarines the body of the parasite, when lodged 

 within the blood-corpuscle, is enclosed in a distinct capsule or mem- 

 brane, which may be of considerable thickness, and often stains 

 deeply. When the parasite is liberated from the corpuscle, the 

 capsule may be left behind as a conspicuous enclosure of the cor- 

 puscle which has puzzled some observers, and has even been 

 described as a distinct form of parasite (compare Sambon and 

 Seligmann). In H. bicapsulata the capsule is thickened at the two 

 extremities of the sausage-shaped body to form two caps, plainly 

 visible in the living condition, and staining a bright red colour in 

 preparations made with the Romanowsky-stain (Franca, 712). 



Different species of haemogregarines differ considerably in their 

 appearance and size relatively to the blood-corpuscle in which they 

 are lodged, and distinct genera have been founded on these differ- 

 ences ; but as yet the complete life-cycle is known in so few cases 

 that it is not possible at present to draw up a classification of these 

 parasites that can have any pretence to be natural. 



The following are the principal genera that have been suggested for these 

 parasites. Lankesterdla (Drepanidium) is of very small size, the full-grown 

 vermicule being not more than two-thirds of the length of the blood- corpuscle ; 

 type, L. ranarum (minima), parasitic in the blood- corpuscles of the frog. 

 In Karyolysus the parasite is about the same length as the corpuscle, or 

 slightly shorter ; the generic name is derived from the action of the parasite 

 on the nucleus of the host- cell, which is often broken up and " karyolysed," 

 though not invariably. This form of parasite is especially common in Reptilia 

 Squamata, lizards and snakes ; type, K. lacertarum. In the genus Hcemo- 

 gregarina (sens, strict.) the full-grown vennicule is much longer than the 

 corpuscle, within which it is doubled on itself in the form of the letter U, 

 with the nucleus situated at the bend ; type, H. stepanom of European water- 

 tortoises, Emys lutaria and Cistudo europcea. Finally there are the " leuco- 

 cytozoa " of mammals, for which the generic names Hepatozoon, Miller, and 

 Leucocytogregarina, Porter, have been proposed ; if it becomes necessary to 

 separate them from the genus Hcemogregarina, Miller's name has the priority, 

 as Wenyon (690) has pointed out. The fact, however, of parasitism in a white 



