THE SPOROZOA 



155 



wound filament is the result. The nuclei of the two polar capsules 

 soon degenerate and disappear, leaving only the capsules with their 

 threads, which show a striking similarity to those of the nematocysts 

 of the Coelenterata. The archispore in many cases develops a 

 bivalve shell, and in this condition can remain for some time within 

 the original spore-forming body (pan-sporoblast); or the original 

 membrane may be thrown off, leaving the encapsuled spores sus- 

 pended freely in the endoplasm of the parent organism. In most 

 cases there is no means of exit for the spores from the body of the 

 host until the latter dies. The archispores thus accumulate until 

 great cysts, sometimes as large as 30 mm. in diameter (Zschokke, '98, 



E 



H 



Fig. 86. Myxobolus ; capsule-formation. [THELOHAN.] 



A-D. Division of the sporoblast nucleus. F. The sporoblast is divided into two " sporogenous 

 masses " each containing three nuclei. G. Sporogenous mass with protoplasm of the spore and two 

 masses which are destined to develop into capsules and filaments. H. The threads are first seen 

 as buds in the vacuole. 



Myxobolus bicaudatus), are formed within the tissues of their host. 

 When taken into a new host, the shell of the archispore under suitable 

 excitant, either chemical or physical, soon opens, and the filaments 

 contained within the capsules are thrown out, according to Balbiani, 

 through special apertures, and by the pressure of the capsular walls 

 (Biitschli). These filaments, several times the length of the spore, 

 remain attached, their free ends being swayed about by the currents 

 until they come in contact with and penetrate some cell of the mucous 

 membrane of a new host. The parasite thus anchored retains its 

 position in the lumen until its bivalve shell is thrown off and it can 

 move for itself (Leuckart, Biitschli, Gurley 1 ). 



In the Myxosporidiida, therefore, sporulation is not the final act of 

 a cell-parasite, but takes place while the animal is performing other 



1 For discussion of various views see Gurley ('93). 



