THE SPOROZOA 227 



Finally, in Adelea ovata, as already mentioned, and in Benedenia eberthi 

 (Fig. 58, c), the flagella are totally absent, and the microgamete moves 

 by undulating movements of the whole body. 



Two interesting variations are seen in the condition of the macro- 

 gamete at fertilisation, which add to the striking resemblance between 

 this process in Coccidia and the fertilisation of the ovum in Metazoa. 

 In Coccidium schubergi and many others the macrogamete is naked until 

 the penetration of a microgamete into its substance has been effected, 

 whereupon the oocyst at once commences to be secreted, barring out other 

 microgametes. But in C.proprium, parasitic in newts (Fig. 57), the oocyst 

 is secreted round the macrogamete before fertilisation ; within the tough 

 membrane the protoplasm contracts and is in contact with it only at one 

 point, where a micropyle is formed, a minute pore through which the 

 microgamete enters (Fig. 57, a). When this event has taken place the 

 micropyle is closed up and the protoplasm withdraws from it (Fig. 57, 

 b and c). A fertilisation -spindle occurs in this species, similar to that 

 described above, but apparently less regular in arrangement. Since in 

 Coccidium oviforme of the rabbit the protoplasm of the macrogamete is 

 also contracted and does not fill the oocyst (see Fig. 62), it is not improb- 

 able that the envelope in question is formed before fertilisation as in 

 C. proprium. 



In Cyclospora caryolytica the fertilisation is remarkable for the occur- 

 rence of polyspermy (Schaudinn [5 la]). A great number of microgametes 

 enter the macrogamete, but only one fuses with the female pronucleus, 

 the others being absorbed in the cytoplasm. In other respects the 

 fertilisation is of the usual type, with formation of a fertilisation-spindle 

 and secretion of a tough oocyst round the zygote. 



In the sporogony the greatest variation occurs, and as the modern 

 classifications of the Coccidia are founded entirely upon the character of 

 the spores and their formation in the different types, it is sufficient to 

 refer to the systematic review below for information on these points. 

 It may be noted, however, that the spores of Coccidia are usually of 

 simple form, the sporocysts not prolonged into the tails, spines, or other 

 processes so common in Gregarines and in Myxosporidia, the only excep- 

 tions to this rule being Minchinia chitonis (Fig. 66, a), Echinospora labbei 

 (Fig. 66, c), and Barroussia caudata ; and further, that with very few excep- 

 tions the number of sporozoites present in the Coccidian spore does not 

 exceed four, and seems never to be eight, the usual number in Gregarines. 



(2) Variations in the Life-Cycle. Although there are but few 

 Coccidia, relatively, in which the life-cycle has been studied in full 

 detail, yet some important differences have already been made 

 known between the different species so far investigated. It has 

 already been stated above that Adelea ovata differs from its two 

 colleagues in Lithobius in the important fact that the sporozoites 

 which start the life-cycle in a new host give rise from the first to 

 sexually differentiated schizonts, which proceed to multiply by 

 schizogony for a number of generations before finally giving rise to 

 the gametes. 



