138 



THE PROTOZOA 



from doubt, and in any case parthenogenesis seems to be of much 

 rarer occurrence among Protozoa than among Metazoa.* 



Autogamy, on the other hand,- is a phenomenon which has been 

 frequently observed in Protozoa, chiefly, though not exclusively, 

 among parasitic forms ; it may be defined as syngamy in which the 

 two gametes, or at least the two pronuclei, that undergo fusion 

 are sister-individuals derived by fission of the same parent cell 

 or nucleus. Hartmann (116) has brought together the many cases 

 of autogamy known to occur among Protozoa and other- Protist 

 organisms, and has classified them under a complex terminology. 

 It is sufficient here to mention two typical cases, those, namely, 



of Actinosphcerium 

 and Entamceba coli, 

 made known by R. 

 Hertwig (64) and 

 Schaudinn (131) re- 

 spectively. 



In Actinosvhcerium 

 an ordinary indi- 

 vidual (Fig. 3) be- 

 comes encysted as 

 a multinucleate 

 ' mother - cyst , " 

 which becomes di- 

 vided up into a num- 

 ber of uninucleate 

 "primary cysts," 

 after absorption of 

 about 95 per cent, of 

 the nuclei 'originally 

 present. Each pri- 

 mary cyst then di- 

 vides completely into 

 two distinct cells 

 " secondary cysts." 



Each secondary cyst then goes through a process of nuclear re- 

 duction (see below), after which it is a gamete ; the two gametes 

 then fuse completely, cell and nucleus, to form the zygote. 



* Prowazek (557) has described in Herpetomonas musccR-domesticce a process 

 interpreted by him as parthenogenesis (" etheogenesis ") of mle individuals, bat 

 the correctness both of his observations and of his interpretations are open to 

 the gravest doubt. According to Flu (536), the objects to which Prowazek gave 

 this interpretation are in reality stages in the life-history of a quite distinct 

 organism, named by Flu Octwnorea muscce-dome-iticce, and now referred to the 

 Miorosporidia. It is greatly to be deprecated that interpretations of such un- 

 certain validity should be used, as has been done, to support general theories in 

 the discussion of the problem of syngamy. 



Fro. 73. Autogamy in Entatncd>u colt. A, The amoeba 

 at the beginning of encystation with a single nucleus ; 

 B, the nucleus dividing ; 0, the two daughter-nuclei 

 throwing off chromidia ; a space has appeared be- 

 tween them ; D, each nucleus has formed two re- 

 duction-nuclei, which are being absorbed ; E, a 

 resistant cyst-membrane has been secreted ; the 

 partial division in the protoplasm has disappeared, 

 and the two reduced nuclei are each dividing into 

 two ; F, each daughter-nucleus of the two divisions 

 in the last stage has fused with one of the daughter- 

 nuclei of the other division to form two synkarya. 

 After Hartmann (116), drawn by him from the de- 

 scription given by Schaudinn (131). 



