Papers from the Marine Biological Laboratory at Tortugas. 217 



a longitudinal split, thus leading to the belief that they are true chromo- 

 somes. Kuschakewitsch states that "the chromatin of the nucleus gathers 

 into larger elements, which almost entirely fill up the interior of the nucleus 

 (Kernraum). In some cases there are formed, transitorily, true chromo- 

 somes which exhibit a clear longitudinal split. Then the nuclear membrane 

 disappears and the chromatin elements (karyomerites) lie free in the 

 plasma." The outstanding difference between the processes relative to the 

 breaking down of the nucleus in the two forms is the fact that in Strombus 

 the ultimate karyomerites are not formed within the nucleus while the 

 latter is yet intact. Furthermore, when finally established, they have an 

 extreme variation in size, little uniformity in shape, and never show any 

 indications of a longitudinal split. In short, unlike those of Vermetus, the 

 karyomerites of Strombus can not be said to be chromosomes, nor is it at 

 all certain that they represent an attempt on the part of the chromatin to 

 form chromosomes. 



The further history of the karyomerites is one concerned with processes 

 leading to their vesiculation and, later, to their gradual degeneration and 

 ultimate disappearance. When first scattered into the cytoplasm the 

 karyomerites lie in close contact with it on all sides. Very shortly after- 

 wards, a clear space, one which gradually grows larger, separates them 

 from the surrounding cytoplasm (figs. 20 to 25). The substance filling this 

 space is essentially like nuclear sap and is probably formed by a differ- 

 entiation of the cytoplasm immediately surrounding a karyomerite. A 

 little later a definite membrane can be seen to have been formed around the 

 clear area, separating it and the inclosed karyomerite from the cytoplasm 

 (figs. 26 to 32), It is quite possible that this membrane is formed as a pre- 

 cipitation membrane between colloids of opposite electrical charges. If this 

 explanation is the true one, then the differentiation of the cytoplasm must 

 have been caused by a chemical reaction between itself and the karyomerite, 

 the substance formed acquiring the acid properties of the chromatin. The 

 reaction must continue until the interposition of the formed substance causes 

 too great a separation of the reacting substances. Then, when the reaction 

 has ceased, a precipitation membrane is formed between the acid and 

 therefore positively charged substance resulting from the reaction and the 

 basic and negatively charged cytoplasm. 



After the formation of the membrane, the inclosed karyomerite breaks 

 down into several smaller pieces, each of which takes up a position just 

 beneath the membrane (figs. 26 to 32). In this way a number of chromatic 

 vesicles arise which are very characteristic for the ensuing stages, and 

 which, as will be shown later, persist for a long time before their actual 

 degeneration sets in. Most of the smaller chromatic fragments, however, 

 do not form vesicles but are absorbed without any further changes. 



The disappearance of the centrosome takes place very suddenly and 

 the nature of the process is not entirely understood. Absolutely no struc- 

 tures were found which could be interpreted with any degree of assurance 



