io8 



THE ANIMAL PARASITES OF MAN 



the tissue-parasites often attain a considerable size, so that the integument 

 of the host forms protuberances over them ; they are of a roundish or 

 irregular shape, which does not change, except as regards the alterations 

 induced by growth ; they are usually enveloped in a connective tissue covering 

 formed by the host. 



The protoplasmatic body usually permits the finely granular ectosarc 

 to be distinguished from the coarsely granular endosarc ; occasionally the 

 former is thickened into a kind of integument. In addition to various enclo- 

 sures, there are as a rule numerous nuclei, which divide mitotically, and 

 all originate from the primary nucleus of the early stage (amoeboid germ), 

 enclosed in the spore. 



FIG. 50. Schema of a spore of Myxo 

 bolus : (a) One polar capsule has protruded 

 the filament ; two nuclei and a " vacuole " 

 in the sporozoite ; (b) spore seen in optical 

 section the two polar capsules in the 

 interior (after Doflein). 



The development of the spores commences long before the ultimate size 

 is attained, and in some species their number is remarkably large, in 

 others small, or limited to two only (Polysporea Disporea). The spores 

 (fig. 50) are surrounded by two concave shells, turned facing each other 

 and united at the borders ; the external surface may be smooth or 

 sculptured, and may carry one. or two .caudal appendages at the one 

 pole ; they enclose at the pointed anterior pole two formations resembling 

 nettle-capsules, the polar capsules, the spirally rolled hollow filaments of 

 which may be protruded spontaneously or through the action of certain agents. 

 The posterior larger half of the internal space is occupied by a proto- 



FIG. 51. Myxidium lieberkuhnii : 

 (a) Pansporoblast, with four nuclei ; 

 (b, c] pansporoblast with eight nuclei ; 

 (d) pansporoblast divided into two 

 sporoblasts, after expulsion of two 

 nuclei ; (e) pansporoblast with 10 

 nuclei (after L. Cohn). 



plasmatic body (amoeboid germ, sporozoite), containing one or two nuclei 

 and a so-called vacuole, which represents the young myxosporidia ; it 

 becomes free in consequence of the bursting open of the two halves of the 

 shell, and then can execute amoeboid movements (fig. 53). 



The spores are formed by a portion of protoplasm (pansporoblast) 

 gathering round each nucleus of the parent (sporont), the nucleus again 

 repeatedly dividing until eight to ten daughter nuclei rarely more are formed 

 (fig. 51) ; the protoplasm of the pansporoblast then divides into two halves 

 (sporoblasts), in which the nuclei are equally distributed after two -of 

 them have been extruded. Accordingly, each sporoblast contains at least 



