TUB PARASITE MIXCHINIA. 449 



pax'ticles can be ingested by the plasmodia as by an ordinary 

 amoeba. Masses of fibres staining black with iron hfeaiatoxvlin 

 may sometimes be seen enclosed in an active plasmodium. They 

 either disappear before encystment, or sometimes they may be 

 extruded in a mass directly after the formation of the cyst, and 

 become compressed between it and the parasite. Further, certain 

 deeply staining granules are generally contained in the cytoplasm, 

 round which no clear space can be observed as round a nucleus. 

 These granules are easily distinguished from nuclei when the 

 latter assume the vesicular form after encysting (PI. I. figs. 1 

 & 3, gr.), although it is almost impossible to distinguish them 

 before this change is affected. Caullery and Mesnil (2, fig. 11) 

 saw similar chromatic bodies left over after the nuclei had become 

 vesicular, but interpreted them as degenerate nuclei. In 

 Minchinia they seem likely to be unassimilated particles, possibly 

 remains of host-cells, taken in during the active life of the 

 Plasmodium. In one case it was practically certain that the 

 parasite had ingested a host-cell — apparently a phagocyte ! In 

 many cases these cells apply themselves so closely to a plasmodium 

 that it is difficult to see any boundary between them (fig. 2). 

 Cuenot (6) has recently given some useful information about the 

 activities of the phagocytes of Chiton, and usually there is no 

 difficulty in distinguishing the nucleus ot" one of these cells from 

 a pai'asite nucleus. In Minchinia, however, certain plasmodia 

 occasionally appeared at first sight to be giving off buds in which 

 the nucleus had assumed a vesicular form ; but after further 

 study I am convinced that these specimens were really only 

 plasmodia to which host-cells were endeavouring to attach them- 

 selves. Gemmation has, however, been described by Svvai-czewsky 

 (18) as a mode of reproduction, in addition to plasmotomy, in 

 certain Ichthyosporidia. 



Sporogony. 



(1) Formation of gametes. 



When the host has become strongly infected most of the 

 plasmodia draw in their pseudopodia and become rounded off and 

 encysted. It seems possible, from the consideration of after-events, 

 that two plasmodia may mingle before encysting, but no direct 

 evidence has been forthcoming on this point. A thin pellicle is 

 secreted, but in most cases this is soon covered and obscured by 

 the host's amoebocytes, which apply themselves to it, becoming 

 gradually flattened out to form a cellular cyst around the parasite. 

 This cyst is generally only one cell thick (PI. I. figs. 3 & 4J, and its 

 nuclei become more and more flattened with growth. Occasionally 

 there may be four or five layers of cells forming a thick cyst 

 round a parasite, but this is an abnormal condition. The cysts 

 are spherical, and vary very much in size, but they are not 

 generally moi'e than 75 p, or less than 40//, in diameter. The 

 nuclei assume a vesicular form, and probably enter upon a resting 



