252 THE PROTOZOA 



It appears, therefore, that the nuclear membrane in Protozoa can 

 have nc great significance, since it may be absent altogether (dis- 

 tributed chromatin), present only during resting phases (Sporozoa), 

 or persistent throughout all changes of the cell. When present, it 

 may be formed, apparently, from the cytoplasmic reticulum (Noctiluca), 

 or from the nuclear reticulum {Actinosphczrium, Reticulariida, Cocci- 

 diida), and these observations are in line with the results obtained by 

 numerous workers upon the nuclei in Metazoa. 



B. The Linin Network 



Many protozoan nuclei are permanently in the condition repre- 

 sented by Schaudinn's first stage of the nucleus of Calcituba (Fig. 134), 

 and like this possess neither membrane nor linin reticulum, consist- 

 ing throughout of chromatin (many phytoflagellates). When, how- 

 ever, a membrane is present, there is usually a clear area with little 

 or no trace of structure (some Heliozoa, Penard, '90), or else a well- 

 defined reticulum between the membrane and the chromatin. The 

 reticulum has been observed in nuclei of every class of Protozoa, as a 

 fine meshwork similar to the cytoplasmic network, and to the 

 linin reticulum of tissue nuclei. In many cases, however, the 

 chromatin granules are not embedded in such a reticulum, but 

 form a central mass in the nucleus. In other cases, and frequently 

 during preparation for division, the granules are dispersed throughout 

 the reticulum, which then appears like a typical nucleus {e.g. Actino- 

 spharium, Fig. 140). In some forms the linin-threads are so 

 extremely minute, and the chromatin granules so large, that it appears 

 incredible that the latter should be inclosed in the former, as is gen- 

 erally believed to be the case in the nuclei of Metazoa. In many 

 macronuclei, the structure of the linin and chromatin, on the other 

 hand, is like that of tissue-cells. In nuclei with a firm and re- 

 sisting membrane, as in Amoeba proteus, there is little room for 

 belief that the cytoplasmic and nuclear contents are connected, and 

 the two parts appear to be quite different in structure. This 

 nucleus and a few others show no trace of the linin reticulum, 

 but contain at least two kinds of granules which make up the bulk of 

 the chromatin and ground substance or karyolymph. Noctiluca 

 ■miliaris (Fig. 141, E) has a nucleus of this type with large granules 

 which stain intensely with acid dyes (Ishikawa, '94; Calkins, '98). 

 The granules may possibly represent the cedematin-granules which 

 Reinke ('94) distinguished in the nuclei of Metazoa, or possibly they 

 represent a diffuse or distributed nucleolus, as Balbiani ('90) assumed 

 in regard to the nucleus of Loxophyllum meleagris. Doflein ('00) 

 maintained that this nucleus possesses a distinct linin network which 



