THE SPOROZOA 163 



colour reaction with sulphuric acid and iodine, and are there- 

 fore recognised as belonging to the class of starches. They 

 must be regarded as a store of reserve food material stored 

 up in preparation for impending reproductive processes. The 

 nucleus is lodged in the endoplasm. It is a spherical body, 

 with a distinct nuclear membrane and clear contents. In the 

 latter are several deeply staining bodies, resembling nucleoli, 

 but as each consists of a corpuscle of achromatic plastin with 

 which a certain quantity of chromatin is associated, they are 

 called karyosomes, to distinguish them from true nucleoli 

 which consist of plastin only. The Sporozoa are probably 

 degenerate in consequence of their parasitic habit, and 

 accordingly we find that Monocystis has no pseudopodia, no 

 flagella or cilia and no contractile vacuole. 



The foregoing description refers only to the full-grown 

 individuals of Monocystis ready to enter upon the reproductive 

 phase of their life history. Previous to this there was a period 

 of inactivity during which the animal absorbed nutriment, 

 grew in size and stored up the granules of reserve material 

 in its endoplasm. In the sub-class Telosporidia, to which 

 Monocystis belongs, this period of purely vegetative growth 

 is sharply marked off from the period of active reproduction 

 that follows : it may therefore conveniently be referred to as 

 the trophic phase of existence, and each individual parasite 

 during this phase may be called a trophozoite. The earliest 

 known stage of the trophozoite of Monocystis agilis is a 

 minute nucleated corpuscle of protoplasm lodged in one of 

 the mulberry-shaped cell-masses formed by the developing 

 spermatozoa of the earthworm (fig. 34, J3). The last-named 

 are formed by the repeated divisions of a sperm-mother cell ; 

 but instead of the whole of the protoplasm going to form 

 spermatozoa, a central cylinder of residual protoplasm, the 

 * sporophore, is left, to which the heads of the spermatozoa are 

 attached. It is in this sporophore that the young trophozoite 

 lives and, absorbing its contents, grows up into the mature 

 form. The development of the spermatozoa proceeds, in 

 spite of the presence of the parasite, and the latter eventually 

 appears to be clothed by a coat of long cilia, which are, in 

 fact, the tails of the spermatozoa, now withering for want 

 of nutriment. The young trophozoite is therefore a cell- 

 . parasite and only quits its cell-host to wander free in the 



