SPOROZOA. 55 



changing their form, while others are amoeboid. They vary much 

 in size, some not exceeding ten micromillimetres in length, while 

 others may attain a length of sixteen mm. The protoplasm 

 usually exhibits a differentiation into ectoplasm and endeplasm, 

 and the endoplasm is often highly granular a feature which 

 becomes more marked with the age of the individual. 



Conjugation occurs in some groups (Gregarinida, Drepanidiidia, 

 etc.), but has not been observed in all. 



Reproduction is effected by the division of the protoplasm into 

 spores, which may be coated or naked. In most cases encystment 

 precedes sporulation, but in some of them the spores are produced 

 gradually during the ordinary life of the individual. In the 

 Gregarinida and Coccidiidea the spore-protoplasm divides to form 

 the young forms. In others the whole spore becomes the young 

 form. There is often a little residual protoplasm generally non- 

 nucleated left over after the sporulation. The young which issue 

 from the spores are either falciform or amoeboid. 



In Gregarinida and Coccidiidea the sporulation usually takes place 

 after the cyst has left the host (exogeny), but in the other forms 

 it is effected within the host (endogeny). 



A process which may or may not be analogous to the formation of polar 

 bodies of the metazoan ovum (or speaking more generally, to the reduction- 

 divisions of the progametes) has been observed by Wolters in Gregarines (Arch. 

 Mic. Anat. Bd. 37) and by Labbe (loc. cit.) in Coccidia. The nucleus divides ; 

 one half remains in the animal, while the other passes to the surface and 

 disappears. This phenomenon precedes the fusion of the nuclei in the con- 

 jugating gregarine, and sporulation in the Coccidia. 



In Gregarinida and Coccidiidea the cysts pass out with the faeces 

 and enter another host in its food. In the other orders the method 

 of transference from host to host is not certainly known, but 

 probably in some cases the spores are not able to leave the host 

 until its death, after which they may enter a new host in the food ; 

 while in other cases it is possible that the infection is transmitted 

 by blood-sucking insects, or through the lungs in dust. 



It is possible that there may be in the exogenous forms at least 

 some other mode of reproduction besides that of spore-formation. 

 Very little is known on this head; but unless there is some other 

 reproductive process, it is difficult to see how in exogenous forms, 

 such as Coccidium oviforme of the rabbit, the enormous number 

 of individuals which characterise acute coccidiosis is produced. It 

 is also probable that in some cases, e.g., the forms which live in 



