MUSEUM OF COMPARATIVE ZOOLOGY. 261 



phylum, and of paucinucleolar nuclei in the lower members of each group 

 (viz. fishes and . reptiles). What is. thus established as a probable order of 

 succession in a phylogenetic sense, is shown to be unquestionably true in the 

 ontogeny of certain species, especially in the case of numerous tissues of Musca, 

 where the growth of the larva is accompanied with a corresponding increase of 

 nucleoli from one up to thirty or more. This increase of nucleoli is probably 

 effected by successive divisions of the single nucleolus, and is accompanied by 

 a gradual approximation of the nucleoli to the wall of the nucleus, perhaps as 

 a result of an attractive influence exercised by the nuclear membrane. There 

 are, he thinks, certain important reasons for considering the nucleoli to be of 

 substantially the same nature as the cell protoplasm of young cells, viz.: — 



1. Certain resemblances in their optical conditions; 



% The similayity of their, rpdcye-pheiftie^l.reaetioftsj.^ , 



^•3. Th.e tendency of large nucleoli to vacuolation; .i % . -. 



4. The changes of form (amoeboid) in the nucleoli; a^d especially, 



5. The growth and self-division of the nucleQ]i.',i*,4>7tt«j., 



As a natural deduction the nucleoli are considered as eleftientary organisms, — 

 the equivalents of cytodes, or, if vacuolated, of nucleated cells,* — and the nu- 

 cleus becomes from this point of view a breeding chamber (hohler Brutraum) 

 jp;}wiiidh, the; (endogenous) daughter cells (nucleoli) arise. Finally, attention 

 is drawn to the possibility of identifying the liberation of such endogenous 

 daughter; cells with the histolytic processes described by Weismann. 

 .?; Iji ; extension of Heitzmann's studies on the blood corpuscles of Astacus, 

 jPfiOMMA^iN ('75, pp.i 289-294) has: produced very interesting drawings of the 

 nticlear and cellular reticulum met with in cells, which are probably also blood 

 corpuscles of Astacus, though I believe no definite statement is made as to 

 the source of the cells figured. Frommann was unable to verify Heitzmann's 

 observation as to the method in which the vacuolated grains give rise to a 

 closed system of network, especially since it could not with safety be denied 

 that the apparently hyaline protoplasm took part in the formation of its 

 filame^Lts., ... 



The study, of thoracic ganglia in the crayfish yielded results confirmatory of 

 st^^emeiits made^ by him in a previous paper. The membrane of the nucleus 

 is not of .uniform . thickness ; there are, namely, within the nucleus granules 

 and nucleoli which are closely apposed to, or fused with the membrane. The 

 nucleoli are from three to ten in number, oval, round, or 3- to 4-angled, and 

 may contain a more highly refringent grain in the centre. The angles are 

 drawn out into coarse fibres, and there are, beside, finer threads connecting the 

 nucleoli to surrounding granules, which in turn are joined to each other by 

 short filaments. The nucleoli may be replaced by compact grains and fine 

 granules. The filaments of the cell protoplasm unite with the nuclear mem- 

 brane, with granules in it, or with nuclear granules lying inside the membrane, — 

 in short, a direct connection between intra- and extra-nuclear network. 



* This recalls the view which Vogt (*42) entertained-eoncerning- the nature of the 

 ^* Keimflecke" of the germinative vesicle in fishes and amphibians. 



