382 JULIA ELEANOR MOODY 



called aniphinucleus of Goldschmidt; second, a type, illustrated 

 by Arcella, Centropjocis and others, in which chromatin material 

 is extruded from the nucleus to form the chromidial-netz of 

 Hertwig, or the idiochi-omidia of Mesnil ('05); third, a type in 

 which there is a complete separation of the two elements into 

 distinct masses, represented by the macro- and micro-nucleus 

 of many infusoria. 



Although this complete separation of nuclear material is of 

 common occurrence among the infusoria, it is by no means 

 universal. An examination of the family Enchelinidae in Biitsch- 

 li's "Protozoa" shows that in the description of fourteen genera, 

 the presence of a micronucleus is positively stated to occur 

 only in the case of Didinium. Among the others, micronuclei 

 have either not been observed or have been little studied. Gold- 

 schmidt's opinion that the infusoria show a primitive nuclear 

 condition is opposed by Dobell, who looks upon the complete 

 separation of chromatin substance as another indication of the 

 high specialization shown by these organisms, rather than a 

 simplification as advocated by Goldschmidt. According to 

 Dobell, all functions, somatic and propagative, are resident in 

 the same living nuclear molecule, one or the other predominating 

 in the course of cell differentiation. 



It sometimes happens that the separation of the two mate- 

 rials is but temporary. Neresheimer ('08) describes the inter- 

 esting case of Ichthyophthirius, in which the nucleus buds off 

 a smaller nucleus, which divides, each part undergoing two 

 reduction divisions. Three of the resulting micronuclei degen- 

 erate. The fourth divides again forming two micronuclei which 

 fuse. The zygote thus formed re-enters the original nucleus 

 and fuses with it. We have here evidently a modification of 

 the first type described, in which both functions are combined 

 in the same body. 



Considerable confusion has resulted from the use of the term 

 'chromidia' applied by Hertwig to the nuclear substance ex- 

 truded by Actinosphaerium when starved or overfed. The 

 chromatin in this case was the direct result of nuclear fragmen- 

 tation brought about by abnormal conditions in the enviromnent 



