166 CONJUGATION, MATURATION, AND FERTILIZATION 



nophrys sol and Actinos'phermm eichhornii (see Figs. 63, 65) the 

 former exogamic, the latter endogamic, similar divisions may occur, 

 two degenerating nuclei being formed in actinospherium, but only 

 one in actinophrys, a result which led Hertwig ('98) to believe that 

 Schaudinn ('96) had overlooked one of the division stages. In 

 gregarines there is evidence to indicate that the preliminary divisions 

 are not of the nature of reducing divisions, but are qualitative, whereby 

 idiochromidia or germinal chromatin is separated from vegetative. 

 Thus, in Leger's beautiful work on ophryocystis ('07), the nuclei 

 divide twice before the internal bud or gamete is formed, one of the 

 products of this division becoming a somatic or nutritive nucleus of 

 the parent cell, the other a "reduction" nucleus (Fig. 80). 



In foraminifera and in fresh-water rhizopods reducing divisions do 

 not occur, but a "primary" vegetative nucleus remains unused and 

 degenerates in the residual body. Other instances of the elimination of 

 chromatin from all subdivisions of the protozoa might be cited, but 

 among them there are but few cases where the characteristic meta- 

 zoan conditions prevail. Certainly, the so-called reducing divisions of 

 the iBxyosporidia are not analogous, for here, according to Schroder 

 ('07) and Keysselitz ('08), fourteen nuclei are formed, ten of which 

 are "somatic," two of them degenerate, while two only remain to 

 conjugate (Fig. 61); nor are they in the actinomyxida;, where 

 Caullery and Mesnil ('05) found eighteen nuclei arising from the 

 single primary nucleus, two of them somatic and sixteen germinal, 

 the latter conjugating two by two. 



Such a list might be further enlarged by the addition of case after 

 case of so-called reducing divisions, scarcely a paper being published 

 on the reproduction of protozoa that does not describe some such 

 process. But in none of them is there sufficient evidence of the forma- 

 tion and division of chromosomes, and until such evidence is forth- 

 coming we cannot draw accurate comparisons between the processes 

 of maturation in protozoa and in metazoa. In a few cases, however, 

 notably among the infusoria, definite maturation chromosomes are 

 formed and divided, and here we find the nearest approach to the 

 conditions in metazoa. They were first seen and correctly interpreted 

 by Biitschli ('76), while numerous observers (Balbiani, Maupas, 

 Hertwig, Hoyer, Hamburger, Prandtl, Popoft", and others) have since 

 added little by little, until, in some cases, notably in Paramecium 

 aurelia (caudatuni), the phenomena may be brought directly in line 

 with those of the metazoa. 



In Paramecium, as in other dilates, the idiochromatin is separated 

 at an early stage from the vegetative chromatin, occurring with the 

 third division of the fertilized micronucleus when macronuclei and 

 micronuclei are differentiated. 



The raacronucleus of the cell plays absolutely no part in the conjuga- 



