SPOROZOA 



I07 



B 





cold-blooded animals. They are at least binucleate in the youngest 

 free state, and become large and multinucleate apocytes, which 

 may bud off outgrowths as well as reproduce by spores. The 

 spores of the apocyte are not produced by simultaneous breaking 

 up, but by successive differentiation. A single nucleus aggregates 

 around itself a limited portion of the cytoplasm, and this again 

 forms a membrane, becoming an archespore or a " pansporoblast," 

 destined to produce two spores ; within this, nuclear division 

 takes place so as to form about eight nuclei, two of which 

 are extruded as abortive, and of the other six, three are used 

 up in the formation 

 of each of the two 

 spores. Of these 

 three nuclei in each 

 spore, two form 

 nematocysts, like 

 those of a Coelen- 

 terate (p. 246 f.), at 

 the expense of the 

 surrounding plasm ; 

 while the third nu- 

 cleus divides to form 

 the two final nuclei 

 of the reproductive 

 body. The whole 

 aggregate of the reproductive body and the two nematocysts is 

 enveloped in a bivalve shell. In what we may call germination, 

 the nematocysts eject a thread that serves for attachment, the 

 valves of the shell open, and the binucleate mass crawls out and 

 grows afresh. Nosema hombycis Nageli (the spore of which has 

 a single nematocyst) is the organism of the " Pebrine " of the 

 silkworm, which was estimated to have caused a total loss in 

 France of some 40,000,000 before Pasteur investigated the 

 malady and prescribed the effectual cure, or rather precaution 

 against its spread. This consisted in crushing each mother in 

 water after it had laid its eggs and seeking for pebrine germs. If 

 the mother proved to be infected, her eggs were destroyed, as the 

 eggs she had laid were certain to be also tainted. Balbiani com- 

 pleted the study of the organism from a morphological standpoint. 

 Some Myxosporidiaceae produce destructive epidemics in fish. 



* 



Fig. 36. : A, Myxidium lieberkiihnii, amoeboid phase ; B, 

 Myxobolus mulleri, spore with discharged nematocysts 

 {ntc) ; C, spores (psorosperms) of a Myxosporidian. 

 ntc, nematocysts. (From Parker and Haswell.) 



