MORPHOLOGY AND TAXONOMY OF THE SPOROZOA 549 



The free or eelozoic forms are the most generalized in structure 

 and the tissue parasites are generally regarded as having been 

 derived from them by adaptation (Auerbach, 1910; Doflein, 1916; 

 Davis, 1917, et ah). They are somewhat more numerous than the 

 tissue-dwelling forms, Kudo enumerating 125 species of the former 

 and 1 14 of the latter while 3 species are apparently transitional and 

 7 of unknown habitat. The free forms often show a remarkable 

 resemblance to amebae; ectoplasm and endoplasm are usually 

 differentiated, the former, as in some amebae, forming a continuous 

 cortical zone about the organism or, as in other types of amebae, 

 evident in certain regions only. It is occasionally provided with 

 bristle-like processes and the pseudopodia of different types are 

 invariably derived from it (Davis). 



The endoplasm is more fluid than the ectoplasm, contains many 

 nuclei and metaplasmic bodies in the form of fat globules, pigment 

 granules and crystalline bodies, in some cases embedded in struc- 

 tures which under the name of spherules (Davis) are sometimes so 

 abundant as to give a characteristic appearance to the organism 

 (Fig. 220). 



Like other Sporozoa, the Myxosporidia are highly prolific and 

 adaptations to this end are well marked. Asexual reproduction 

 occurs by simple division or by multiple division (plasmotomy) 

 and by budding. Exogenous budding described by Cohn (1896) in 

 My.vidiiim lieberkuhni is regarded by Davis (1916) as abnormal and 

 without significance in reproduction but internal or endogenous 

 budding occurs in Sinuolinea dimorpha Davis, where free cells are 

 formed about nuclei in the endoplasm. These cells, called "gem- 

 mules" by Davis, escape from the parent organism and develop into 

 individuals (Fig. 121, p. 232). 



Propagative reproduction involves the formation of spores and 

 the nearest approach to sexual processes to be found in the Cnido- 

 sporidia. The process has been described by various observers and 

 the general agreement of these descriptions indicates a common 

 plan throughout the group. Schroder's account of sporulation in 

 Sphaeromy.va sabrazesi Laveran and Mesnil may be selected as an 

 example for the entire Order. This form is parasitic in the sea-horse, 

 Siphonostoma rondeletii, and like many others has dimorphic nuclei 

 distinguishable by size and structure. Small areas become differ- 

 entiated within the endoplasm and contain two nuclei, one of each 

 type. These areas, the so-called pansporoblasts, are the mother- 

 cells of the spores. Each nucleus divides in such order that seven 

 nuclei arise from each; the mother-cell then divides into two cells 

 which are destined to form two spores. Each of these cells has 

 7 nuclei, 1 of which is cast out as a "reduction" nucleus; 2 are 

 involved in the formation of the two valves of the spore and ulti- 

 mately disappear; 2 are connected with the elaboration of the polar 



