64 BIOLOGY OF THE PROTOZOA 



type having uniform chromatin granules distributed upon a regular 

 reticulum and with nucleoli of irregular form and size throughout its 

 substance. According to Calkins there is no evidence of a chromatin 

 reticulum, but the massive character of the nucleus is due to the 

 presence of relatively large and stifi' colloidal masses of intra-alveolar 

 material while the chromatin is aggregated in the form of ten or 

 eleven irregularl^^ distributed masses which were called "chromatin 

 reservoirs" but which appear to be multiple endosomes. That 

 these masses consist of chromatin is clearly indicated by the fact 

 that they fragment into chromomeres prior to division and that the 

 chromomeres form the characteristic and unmistakable chromosomes 

 of the nuclear spindle (Fig. 52, p. 101). These diverse accounts of 

 the nuclear structure of Noctiluca indicate the possibility of regional 

 varieties of this universally distributed species. 



Mention may be made here of the vesicular nuclei which arise by 

 a process of so-called free-nuclei formation, the evidence for which 

 is difficult to interpret otherwise. It rests, in the main, on the 

 observation of Hertwig as early as 1876, and again in 1899; of 

 Schaudinn in 1903; of Lister, 1905; of Goldschmidt in 1907; Elpati- 

 ewsky in 1907, and Swarzewski in 1908. In all cases the free 

 nuclei arise by the association of chromidia or chromidiosomes 

 which have been derived from the nucleus and distributed in the 

 cytoplasm. Both Elpatiewsky and Swarzewski describe the for- 

 mation of the minute gametes of Arcella vulgar is by the fragmen- 

 tation of the cytoplasm into minute cells about these free nuclei. 

 These gametes moxe off as minute amoebse leaving the parent with 

 its "primary" nuclei, which ultimately degenerate. Each of these 

 gametes contains at first a few scattered granules derived from the 

 chromidial mass which ultimately unite to form the gamete nucleus. 

 The process is more minutely described by Goldschmidt in connection 

 with the mastigamoeba MasUgeUa vitrea. Here a chromidial mass 

 forms on the outside of the nuclear membrane by transfusion of 

 chromomeres (Fig. 27). After separation of this mass from the 

 nucleus, the chromomeres come together in groups and form nuclei 

 about which minute gamete cells are cut out from the cytoplasm 

 while the primary nucleus remains intact. A somewhat similar mode 

 of formation of the microgamete nuclei of Coccidiimi scJmbergi was 

 earlier described b}'^ Schaudinn. This t^T^e of nucleus formation, 

 according to Minchin, represents the possible origin of Protozoa of 

 "cellular grade" from bacteria-like organisms of non-cellular grade, 

 in which the chromatin is permanently distributed. Doflein (1916) 

 remains skeptical in regard to this t}T)e of free-nuclei formation and 

 Kofoid (1921), apparently without investigation of free-living forms, 

 maintains that such free nuclei are intracellular parasites. It is evi- 

 dent that the burden of proof here rests with the critics. 



In the massive type of nucleus the chromidiosomes are usually of 



