LIFE-CYCLE OF " CYSTOBIA " IRHEGULAIUS (mINCH.). 37 



ago-regatiou {a., fig. 16) surrounding tlie pai-asite ; it is seen, 

 however, in fig. 38 a (/. m.) between the cytoplasm and the 

 layer of nuclei. On the other Land, Avhen the cyst is sporu- 

 lating', I find a much more distinct ectocyst than ever occurs 

 in C. irregularis. External to the endocyst, which corres- 

 ponds, in this case also, to the original limiting membrane, is 

 a pale but firm and homogeneons-looking layer [ect., fig. 44 e); 

 this represents a true outer cyst-membrane. Outside, again, 

 is the nuclear layer, which has now become rather broken 

 down. 



The spore-containing cyst, which is viewed whole in fig. 43, 

 is attached to one of the vascular strands mentioned above 

 (p. 14) ; it is surrounded by an enormous number of cells 

 Avhicli have migrated to the locality. Ej). is the coelomic 

 epithelium attaching it to the strand (sf.), and c.a. is the 

 cellular aggregation around the parasite, the nuclei being 

 closely packed just outside the cyst-wall {cac). Whether 

 these are phagocytic cells or not, they do not appear to have 

 done any injury to the Gregarine, as the contents of the cyst 

 are quite normal. 



(h) Fragmentation of the karyosome. 



Owing to the diflSculty of obtaining material at the time 

 of the year when sporulation genei-ally begins and the rela- 

 tive scarcity of ripe trophozoites (sporonts) in the material I 

 examined, I have, unfortunately, considerably fewer stages 

 showing the nuclear changes at the commencement of multi- 

 plication than I should have liked.^ Still, thanks to a few 

 fortunate preparations, which I have not the least reason to 

 consider as otherwise than perfectly normal, and which fit in 

 quite well with each other, I have been able to obtain a fairly 



> Many recent writers have commented upon their inability to obtain the 

 earliest phases in nuclear division (compare Brasil [3], Cuenot [10], Leger 

 [22], and Paehler [29] ) ; it will be readily understood, liowever, that the 

 diflSculties are enhanced in working with marine hosts, and especially where 

 it is impossible to follow the process in vivo. 



