KARYOKINESIS. 71 



metamorphosis the sphere substance remains distinct from the remaining cell sub- 

 stance and in this respect resembles the archoplasm of Boveri, though spindles are 

 not formed out of it. It has been known variously as "sphere," " Nebenkern" 

 "Centrodeuioplasm' (Erlanger) ; Meves proposes to call it Idiozome. It is formed 

 from eliminated chromatin; as to its origin he says : — (Meves '94, p. 158) " Einen 

 anderen Theil des eliminirten Chromatins, der nicht zur Bilding eines Nebenkerns 

 verwandt wird, findet man in den Sperm atogonien des Salamanders nach meiner 

 Beschreibung in dem die Sphare representirenden' Kdrnerkranz ; in einem bestimm- 

 ten Stadium des Processes sind kleinste Chi-omatinkugelchen von einem Hof von 

 Sparensubstanz umgeben." Again (p. 159) : — " Spater scheint das Chromatin seine 

 Reaction zu andern und in dem Aufbau der Sphare mit einzugehen." 



The idiozome is found particularly, perhaps exclusively, in male sexual cells, 

 and Meves agrees with Kostanecki and Siedlecki, Erlanger, Lenhossek and Mont- 

 gomery, that it cannot be homologized with the sphere of egg cells, though, perhaps, 

 it is homologous with the yolk nuclei of ovarian eggs. Unlike the attraction sphere 

 of van Beneden it is (1) not radiating in structure, (2) only present in resting stages, 

 not in mitosis, (3) sharply limited from surrounding cytoplasm. In spite of these 

 differences I make bold to say that the spheres which I have observed in gasteropod 

 eggs are certainly homologous with Meves' idiozome. To recall only a few of the 

 resemblances : — (1) Both arise (in part) from eliminated chromatin which changes 

 its staining reaction. (2) Both have the same relations to the centrosomes and 

 central spindle. (3) Both persist and preserve their individuality through the 

 entire resting period and even into the following mitosis. (4) Both show a corti- 

 cal and a medullary zone. (5) Both are sharply delimited from the cytoplasm. 

 (6) Neither has radiating structure during the rest stage. (7) Both ultimately dis- 

 integrate and are scattered as coarse granules immediately under the cell membrane. 



The sphere in these gasteropods is derived from an undoubted attraction sphere, 

 with radial structure and without sharp demarkation from the cytoplasm. I con- 

 clude, therefore, that the term idiozome should be extended so as to include the 

 spheres present in all resting cells, or that it should be abandoned altogether. Since 

 it represents, in gasteropod eggs, merely the resting stage of the sphere, it seems to 

 me no more entitled to a specific name than the resting nucleus. 1 



4. Archoplasm. — Of late there has been much discussion of the Archoplasm 

 hypothesis of Boveri ('88) and the general conclusion seems to be that this hypothesis 

 is untenable {cf. Heidenhain, Kostanecki, Erlanger, Wilson, R. Hertwig, Carnoy 

 and Lebrun, et al.) This conclusion is based on the proposition that there is no 

 peculiar substance such as Boveri's hypothesis supposes. Boveri ('95) himself 

 admits that he has been unable to find archoplasm except in the eggs of Ascaris 

 and in Noctiluca. 



The principal features of Boveri's archoplasm hypothesis are the following {cf 

 Wilson, '95, p. 444) : — (1) A specific substance, distinct from other cell constituents, 



1 R. Hertwig ('99) expresses the view that idiozome, spheres, centrodeutoplasm, Nebenkern, etc., 

 are only giant centrosomes or centrospheres. 



