PHENOMENA A CCOMPA N YING FER T I LIZ A TION 



525 



(?) of Trichunyinpha campanida. This is incomprehensible on any 

 interpretation of these nuclear elements as chromosomes in reduc- 

 tion but may be explained as pseudo-reduction and without any 

 connection with meiosis. 



In few ciliates in which the number of chromosomes can be 

 counted, does this first division result in reduction to one-half the 

 number. Gregory (1923) gives evidence that this is the case in 

 O.vytricha fallax and MacDougall in Chilodon iincinatits (Fig. 217). 

 In Paramecmm the chromosomes are short rods too numerous to 

 count. According to the earlier view in regard to the origin of 

 the first s])indle from the crescent it was generally assumed that the 

 first division is transverse. The rods are double, however, when 

 formed and the first division is evidently the separation of these 

 two parts, but whether or not it is a reduction division cannot be 

 determined. According to Dehorne (1920) there is no reduction 

 at any stage as there are no chromosomes. 



f. 



Fig. 218. — Uroleptus mobilis. The second moiotic division and reduction in number 

 of chromosomes during conjugation. (After Calkins.) 



3. Phase C. The Second Meiotic Dnmow.— Prior to Prandtl's 

 work on Didinhim there were no conclusive obser^'ations on the 

 reduction of chromosomes in ciliates. He found that the 16 

 chromosomes characteristic of the first maturation division become 

 reduced to S with the second division. Since his work appeared 

 there have been a number of authentic observations along the same 

 line. Thus Enriques (1907) found a reduction in number from 

 16 to 8 chromosomes in Opercularia coarctata and the same observer 

 (1908) described a reduction from 4 to 2 in ChUndon uncinatvs 

 (Fig. 217), reduction occurring at the second division. Other cases 

 of the same t\'pe are Carchesium poJyinnwn (Popoft", K,'08) with 

 reduction from 16 to 8; Anoplophrya hranchiarvm (Collin), from 

 6 to 3; and UroJepius (Calkins 1919)'from 8 to 4 (Fig. 218). In all 



