SPECIAL MORPHOLOGY AND TAXONOMY OF INFUSORIA 375 



absorption in the cell. The "microchromatin" on the other hand 

 is functional chirinoj sexual phases. From these considerations it 

 would appear that the dimorphic nuclear conditions of ciliates 

 generally is here represented by each nucleus, a parallel being the 

 condition of nuclei in Blepharisma undulnns (Calkins, 1912) where 

 the macronuclei with micronuclei enclosed, arise by diffusion of 

 chromatin from products of the amphinucleus (p. 69). 



In their sexual phenomena also, the Opalinidte differ from the 

 majority of other ciliates. Individuals begin to divide rapidly with 

 decreasing size until minute forms result with one, two or more nuclei 

 according to species (Nerescheimer, Metcalf). These encyst, the 

 cysts passing out with the feces. Tadpoles ingest the cysts which 

 open in the rectum giving rise to the same t\pe that had previously 

 encysted. These now multiply, ultimately forming macrogametes 

 and microgametes which fuse on contact. The zygote has one 

 nucleus at first which later gives rise to the binucleated or multi- 

 nucleated forms, although the exact manner has not been described 

 (Metcalf, 1923). 



Reproduction in ciliates generally is typically by binary cross- 

 division and involves a renewal of motile organs, at least this is the 

 case in forms with cirri, and MacDougall (1925) gives evidence to 

 indicate that cilia also are similarly renewed. It thus results that 

 motile organs of both products of cell division are proportionate to 

 the size of the young individuals. Old metaplastids, as pharyngeal 

 baskets, are discarded and are formed anew in both halves. Nuclear 

 changes during division are quite varied, each species having its 

 own peculiarities of macronuclear condensation and reformation 

 (p. 112). 



Unequal division or budding while uncommon amongst ciliates 

 is the chief method of reproduction among the Suctoria but also 

 occurs in some Vorticellidffi (Spirurhoiia, etc.). In Suctoria, budding 

 is either external or internal, in the latter case the budding area is 

 invaginated, the margins close over, and a brood chamber is formed 

 from which the embryos escape when formed. 



Multiple division or sporulation is also uncommon in the Ciliata 

 but occurs in some of the more generalized, and in some parasitic 

 types. When it occurs it is usually under the protection of a 

 temporary cyst {Colpoda, Ichthyophthirius) . 



Sexual processes are practically universal in the group and the 

 main features of the process are similar throughout. In most cases 

 fusion is temporary and pronuclei are exchanged after which the 

 conjugants separate. In some cases, VorticelUdse, fusion is per- 

 manent and sexual dimorphism is the rule, in other cases such 

 dimorphism is expressed by the pronuclei, but in most cases there is 

 no sex differentiation whatsoever (see Chapter XI). In Trachelo- 

 cerca phcenicopterus , Ichthyophthirius multifilius, and in Opalinidse, 



