550 BIOLOGY OF THE PROTOZOA 



These observations indicate that fertihzation in Myxosporidia 

 belong in the group of autogamous phenomena. In the closely 

 related Microsporidia there is considerable difference of opinion in 

 connection with the time and place of fertilization if it occurs at 

 all. Stempiai (1902, 1904, 1909) and Fantham and Porter (1912), 

 give evidence to indicate that union of nuclei occurs as in Myxo- 

 sporidia and after the spore leaves its capsule. Mercier (1909), 

 Swarczewsky (1914) and others believe that the formation of hetero- 

 gametes oc(;urs prior to sporulation as described by Awerinzew 

 for Ceratomyxa; Debaisieux (1913, 1915, 1916) also believes in a 

 process of autogamy prior to sporulation in Glugea danilewskyi, 0. 

 mulleri, (L anomaht, and in microsporidian parasites of Simulium 

 larvse. 



Similarly a process of autogamy occurs prior to sporulation in 

 Actinomyxida. Here, according to the observations of Caullery 

 and Mesnil (1905) on Sphceraciinomyxon, the youngest stages are 

 found as intestinal parasites of the tubificid worm Clitellio, and are 

 either uninucleated or binucleated. The observers were inclined 

 to believe that the uninucleated stage comes first and that it repre- 

 sents, possibly, a sporozoite. Whatever may be the origin of the 

 binucleated form, the 2 nuclei divide and 2 of the 4 resulting nuclei 

 become somatic nuclei connected with the formation of the cyst 

 wall. The remaining nuclei and cell body now divide until there 

 are 16 independent cells. These unite 2 by 2, fertilization thus 

 occurring endogamously, and 8 spores are finally formed. 



In many of these cases so-called reduction nuclei have been de- 

 scribed as in<iicating processes comparable with chromosome reduc- 

 tion in meiosis. Up to the present time, however, while well-marked 

 chromosomes of definite number have been described by George- 

 witsch (1915) and by Davis (1916) there is no evidence of reduction 

 in number tdther before or after iniclear fusion. Erdmann (1917) 

 has shown that so-called reduction nuclei inside the spore are masses 

 of chromatin or perhaps glycogen, which serve a purpose in the 

 formation of the spore membrane. The extremely minute size of 

 the nuclei and the technical difficulties, make the general problem 

 very difficult to solve in Telosporidia and at the present time 

 there is little prospect of an early solution. 



From the foregoing review it is apparent that the changes of a 

 cumulative character are taking place during the vegetative activi- 

 ties in all types of organization. Such changes are manifested by 

 structural or functional peculiarities at different stages, the most 

 marked of which are at periods of maturity and old age. Some of 

 these are peculiar to certain t}j)es only, e. g., the old age structural 

 differentiations of Mycetozoa and Sporozoa. Others, particularly 

 those occurring at maturity, are more universal but differ in degree 

 in different cases, the least evident being those of hologametes and 



