98 BIOLOGY OF THE PROTOZOA 



further formality, the nucleus meantime assuming an indefinite 

 division figure. More frequently, however, the chromomeres are 

 suspended between an endosome and the nuclear membrane, as in 

 Eimeria schubergi, or various species of Trypanosoma. In some of 

 these, at division the chromomeres appear to form a nuclear plate, 

 and are distributed in equal groups to the daughter nuclei (Fig. 51). 

 In a final group of types of nuclear division figures either from 

 massive or vesicular nuclei, the chromomeres are derived from the 

 fragmentation of endosomes or from a chromatin reticulum. The 

 common feature in this large group is the fact that these chromo- 

 meres unite secondarily to form definite chromatin bodies which 

 satisfy, in part at least, the definition of chromosomes as given above. 

 These chromosomes are divided equally, one-half going to each 

 pole of the division figure. In some cases it is obvious that their 



'^^■W~'^M 



Fig. 53. — Metaphase and anaphase of nuclear division in the radiolarian Aula- 

 cantha scolymantha. X 300. (After Borgert, Zoolog. Jahrbucher, courtesy of 

 G. Fischer.)] 



division is longitudinal, but in the majority of cases it cannot be 

 ascertained with assurance whether their division is longitudinal 

 or transverse. Nuclear figures of this general type may be divided 

 into two groups, in one of which the chromosomes are too numerous 

 to permit of decision as to their constant number, and the second 

 comprising forms in which the chromosomes are constant in number 

 and in some of which this number is reduced to one-half at meiosis. 

 In the first of these groups we would include types like Euglypha 

 alveolata, the various species of Paramecium and some Radiolaria 

 (Fig. 53). In the second group we would place such forms as 

 Actinophrys sol, Aggregata eberthi, Trichomonas and allied flagellates, 

 Trichonympha and related forms, and the majority of filiates in 

 which the maturation processes are known. 



In Euglypha alveolata the chromatin of the vesicular nucleus is 

 distributed throughout the resting nucleus. During the early divi- 



