The effects on the host are confined to the parasitized cells. These generally undergo at first marked hypertrophy and alteration in character; this condition is succeeded by one of atrophy, when the substance of the cell becomes in one way or another practically absorbed by the growing parasite (cf. also COCCIDIA). Since, however, the Gregarines never overrun their hosts in the way that many other Sporozoa do (because of their lack, in general, of the power of endogenous multiplication), the number of cells of any tissue attacked, even in the case of a strong infection, is only a very small percentage of the whole. In short the hosts do not, as a rule, suffer any appreciable inconvenience from the presence of the parasites. Morphology. The body of a Gregarine is always of a definite shape, usually oval or elongated; in one or two instances (e.g. _Diplodina_) it is spherical, and, on the other hand, in _Porospora_ (fig. 3) it is greatly drawn out and vermiform. In many adult Gregarines, the body is divided into two distinct but unequal regions or halves, the anterior part being known as the _protomerite_, the hinder, generally the larger, as the _deutomerite_. This feature is closely associated with another important morphological character, one which is observable, however, only during the earlier stages of growth and development, namely, the presence of a definite organ, the _epimerite_, which serves for the attachment of the parasite to the host-cell (fig. 6). [Illustration: After Siedlecki, from Lankester's _Treatise on Zoology_. FIG. 5.--Part of a section through the apparatus of fixation of a _Pterocephalus_, showing root-like processes extending from the Gregarine between the epithelial cells. g, Head of Gregarine; r, Root-like processes; ep, Epithelial cells.]