450 



THE PROTOZOA 



that found in other Protozoa. In this case, during the ordinary vegetative 

 condition, the generative chromatin representing the rnicronucleus of other 

 Infusoria, and the vegetative chromatin representing the macronucleus, are 

 contained in one and the same nucleus, and become separate only when 

 syngamy is about to take place. The first sign of the separation is the forma- 

 tion of chromidia from the karyosome within the nucleus, resulting in the 

 formation of a secondary nucleus which becomes separate and which behaves 

 exactly as an ordinary micronucleus ; thus indicating a clear homology between 

 the micronuclei of Infusoria and the secondary generative nuclei of Sarcodina. 

 The production of numerous micronuclei in the conjugation of Trachelocerca 



FIG. 188. Formation of micronuclei in Trachelocerca phcenicopterus. A, B, A 

 nucleus has divided into two, and from the karyosome (k. ) of each daughter- 

 nucleus masses of chromatin are being given off into the nuclear cavity ; 

 C, D, the two nuclei of the preceding stages have divided again, to form a 

 group of four, and the chromatin-rnasses (n) have acquired a compact struc- 

 ture and are passing out of the nuclei to form the micronuclei ; in C crystals 

 are seen in the cavities of the old nuclei, probably a sign of degeneration ; 

 E, F, two groups of nuclei, both from the same specimen ; the micronuclei 

 given off from the old nuclei become surrounded by a vacuole (n' in F), and 

 then acquire an alveolar structure (n' in E) ; G, portion of a preparation of 

 the body of a conjugant, the wavy contour on the right being the surface of 

 the body which is in contact with the other conjugant ; numerous micronuclei 

 (n) are seen, and also macronuclei, some of which still appear normal (N), 

 others degenerating (N'). After Lebedew (93). 



is noteworthy, and would appear to favour the theory (see p. 154) that primi- 

 tively numerous gametes (swarm-spores) were produced in the conjugation 

 of Infusoria. 



Examples of a complicated life cycle are to be found in Ciliata chiefly, 

 perhaps solely, among parasitic forms. As an example may be taken Ich- 

 thyophthirius miiUifiliis, a parasite of the skin of various species of fresh-water 

 fishes. In aquaria, where, owing to the limited space, the parasites, if present, 

 find their way to the fish very easily, and where, consequently, a fish becomes 

 infected with vast numbers of the ciliates, the parasites are usually lethal to 

 the host, and cause its death, according to Buschkiel, in about fourteen daj's. 

 In Nature, on the other hand, " ichthyophthiriasis " is seldom observed, prob- 



