metcalf: opalina and the ciliate infusoria 429 



The archaic features of the Protocihata are: (1) the transient 

 character of their pleurinucleate condition, the gametes in the 

 spring becoming uninucleate; (2) the consequent absence of dif- 

 ferentiation of whole nuclei for trophic function (macronuclei) 

 and of other whole nuclei for reproduction (micronuclei) , each 

 nucleus instead containing chromatin of both sorts; (3) the very 

 primitive nature of the contractile vacuole — merely a temporary 

 fusion of some of the axial alveoles to form an irregular and usu- 

 ally branched tubule opening by a posterior pore; (4) binary fis- 

 sion both longitudinal and transverse; (5) sexual union, the com- 

 plete fusion of very dissimilar gametes. A secondary feature 

 is the complete absence of a buccal groove. Numerous genera 

 of Euciliata also show this secondary modification — e.g., Hop- 

 litophrya, Anoplophrya, Discophrya, Chromidina, etc. In both 

 Protociliata and Euciliata this feature is doubtless due to 

 parasitism. 



The author described mitosis in a species of Protoopalina (Opa- 

 lina), discovered by Professor J. H. Powers, whose two nuclei are 

 found resting in a midmitotic condition (anakhase). Awerin- 

 zew described an African species whose usually single nucleus 

 rests in a similar midmitotic stage, and because of its uninu- 

 cleate character named the species Opalina [Protoopalina] pri- 

 mordialis. In the National Musem material is a still more 

 archaic species (as yet unnamed) from Bufo regularis whose 

 single nucleus is in an earlier phase of mitosis than is that of 

 Protoopalina primordialis. Starting with this unnamed species 

 we may arrange the Opalinidae according to their nuclear con- 

 dition : first a species with a single nucleus resting in a mitotic 

 condition but little past the critical (mitotic) phase; then Pro- 

 toopalina primordialis with nucleus in an anaphase condition; 

 then several species with each a single nucleus in a late ana- 

 phase or a telophase condition ; then numerous species each with 

 two distinct resting nuclei; then several species each with two 

 nuclei each of which is just entering upon mitosis; then two or 

 more species each with two nuclei both being in about the critical 

 phase of mitosis; then numerous species each with two nuclei 

 both in an anaphase of mitosis; others with two nuclei each in a 



