MATURATION 



157 



Hertwig), and there are several other forms where much the same thing 

 occurs, e.g., Actinophrys (Fig. 81), Entamceba. In all cases such as 

 these, it is impossible to say whether reduction, in a strict sense, is 

 accomplished, or whether this is merely an elimination of chromatin, for 

 the chromatin is not organized into chromosomes whose precise behavior 

 may be traced ; it is quite likely that there is here no true reduction in 

 the Metazoan sense. In some of the Infusoria, however, definite chro- 

 mosomes are formed in the nucleus during these divisions and a definite 

 chromosomal history may be made out. In Paramcecium, for instance, 

 as described by Calkins and Cull, where the idiochromidia are known as 

 the micronuclei, these alone are concerned in the " maturation " divisions. 

 The micronucleus forms a fairly typical division figure consisting 



FIG. 82. Maturation divisions in Paramcecium aurelia (caudatum). From 

 Calkins and Cull. Only a few of the chromosomes are represented in each case. 

 A. Late anaphase of first maturation division of micronucleus; some chromo- 

 somes incompletely divided. X 1000. B. Early anaphase of second maturation 

 division. X 633. C. Telophase of second maturation division. X 900. 



of a spindle and more than 200 separate chromosomes. During the 

 first maturation division each of these divides longitudinally, the 

 resultants passing in each case to the separate daughter nuclei, without 

 any corresponding division of the cell body (Fig. 82) . A second matura- 

 tion division follows immediately and is precisely like the first giving 

 four daughter nuclei (micronuclei, idiochromidia), three of which then 

 degenerate as in polar body formation. The one remaining nucleus 

 divides again, this time the chromosomes dividing transversely (reducing 

 division?). This third division is not strictly comparable with anything 

 to be found in the Metazoa and is apparently correlated with the charac- 

 ter of the fertilization process in this form, for both parts share in repro- 

 duction. One-half remains in situ as the equivalent (analog) of the egg 

 nucleus, and the other half migrates, as the equivalent (analog) of the 

 sperm nucleus, to the body of another organism, fusing with (fertilizing) 

 the stationary nucleus of that individual. In the majority of the 

 Protozoa the so-called "maturation" or "reduction" divisions are not 



