374 



BIOLOGY OF THE PROTOZOA 



Lumen-(h^'ellino; forms ha^e apparently undergone less degenera- 

 tion than have ectoparasitic types. In the Opalinidse such degener- 

 ation has been the most extreme. Here mouth and other oral 

 structures are entirely wanting and nutrition is osmotic. In the 

 majority of cases however, the peristome and mouth are retained 

 while the cortex is often highl^' sculptured and fantastic as in the 

 Ophry oscolecid je . 



The aberrant Opalinida? are parasitic in Amphibia. Not only 

 are they astomatous but in certain characters they differ widely 

 from other ciliates so that they have been variously placed in 

 classification. Hartog (1900) for example placed them with the 

 Hypermastigida of the flagellates. Metcalf (1918, 1923) includes 

 them as Prociliata and sharply marked off from the remaining 





^^Irrf^ 



Fig. 164. — A, Colcps hirtus; B, Opalina {?) ranarum. (After Blitschli.) 



ciliates. In view of the adaptive changes brought about by a 

 parasitic mode of life, it seems more probable that they are degen- 

 erate rather than primitive types. There are invariably two or 

 more nuclei but the nuclei are identical with no indication of 

 dimorphism (Fig. 104; B). In the nuclei, however, there are two 

 kinds of chromatin according to Leger and Duboscq (1904) and 

 Metcalf (1909 and 1923). The latter distinguishes these types as 

 "macrochromatin" and "microchromatin" the former in mitosis 

 giving rise to band-form "macrochromosomes," the latter to 

 "microchromosomes" in apparently even numbers (from two to 

 ten). The "macrochromatin" is regarded as functional in vegeta- 

 tive life and, like the macronucleus of other ciliates, gives rise to 

 chromidia (Xerescheimer) or otherwise fragments preparatory to 



