206 



THE SPOROZOA 



more commonly than any other Sporozoa, and have long been 

 familiar on account of their frequent occurrence amongst domestic 

 animals, both in birds and mammals, and even in man. They are 

 met with in all the five classes of Vertebrates more or less 

 commonly, and the very numerous species of the type -genus 



Coccidium are almost confined 

 to Vertebrate hosts. 1 In 

 Mollusca, Coccidian parasites 

 are very common in Gastro- 

 poda and Cephalopoda, and 

 Hyaloklossia pekeneeri, Leger, 

 occurs in the kidneys of the 

 Lamellibranch Tellina ; a 

 species, of position as yet 

 doubtful, occurring also in 

 the kidneys of Donax (L4ger 

 [41]). In Arthropods, Coccidia 

 occur sparingly in Insects, 

 more abundantly in Myria- 

 pods, but have not been found 

 as yet in either Arachnida or 

 Crustacea. 



The Coccidia are chiefly 

 parasites of epithelial cells, 

 and since the infection of the 

 host appears to take place in 

 all cases by way of the 

 digestive tract, it is the 

 epithelium of the gut or of its 

 appendages, such as the liver 

 (Fig. 47), that is most often 

 the seat of the parasite. In 

 a considerable number of 

 cases, however, the parasitic 

 germs, after entering the system by way of the gut, go further 

 afield before settling down. Passing through the gut-wall, the 

 parasites are transported, probably, by the circulation of the blood 

 or lymph, to their specific habitat. In those cases in which 

 the vascular system forms the general body-cavity (haemocoele), 

 we find occasionally, though very rarely, what is so common 

 in the Gregarines, namely, Coccidia as "coelomic" parasites. 2 



possible that some of the supposed Coccidia seen in Polychaeta are really intra- 

 cellular stages of Gregarines ; but a genuine Coccidian, Caryotropha mesnilii (Fig. 67) 

 has recently been described by Siedlecki [55a] from Polymnia nebulosa. 



1 Exceptions are two species found in Lithobius forficatus, viz. Coccidium lacazei 

 (Labbe), and C. schubergi, Schaudinn. 



3 An example is Adelea mesnili, Perez, 1899 [50J from the body-carity of 



Fio. 47. 



Section of rabbit's liver infected with Coccidium 

 oviforme, Leuck. After Balbiani, from Wasielewski. 



