[107] EMBRYOGKAPHY OF OSSEOUS FISHES. 561 



and is therefore more depressed. This elevation and depression of the 

 ui)per surface of blastoiaeres in the course of segmentation is often a 

 very marked feature, and gives rise to the most singular superficial irreg- 

 ularity of the whole disk up to the time of the completion of the moiula 

 stage of development. These changes are doubtless due to internal 

 movements of the substance of the blastomeres, dependent upon an in- 

 ternal radial contractile structure. 



The radial and reticulated structure of protoplasm is to Eauber of 

 the most i^rofound significance in relation to the phenomena of growth 

 and development. His conclusions are here, in part, reproduced : 



"1. Radial and trabecular structures of protoplasm are not essen- 

 tially distinct but are manifestations of the same principle, in that the 

 latter is developed as a result of vacuolization, the former in the di- 

 rection of readiest division {spaltharl'eit). 



" 2. The radial and trabecular structure of animal as well as vege- 

 table protoplasm is a factor with which every investigation into the 

 history of the growth of an animal or a vegetable body has to do ; such 

 structure is vitally related to the beginning of development. 



"3. The radial and trabecular arrangement of protoi^lasm grows 

 both by the addition of new material from without, at its peripheral 

 ends, as well as by the incorporation of such material within the pre- 

 existing substance, or both by ai)position and intussusception. Tho 

 protoplasmic streaming necessary for this purpose is facilitated by the 

 interradial i)assages and the corresponding series of spaces in vacuolate 

 l)rotoplasm." 



Of the nucleus he says : 



" The finer phenomena of caryokinesis display to us, in a manner 

 such as does scarcely any other process, working nature at her loom. 

 Groups of granules are the raw material which she next arranges in 

 rows of threads. In astonishment we observe the most manifold looj)- 

 ing and splitting of the granular threads and the completion of the 

 most delicate chromatin structures." * * * "The structure of the 

 nucleus is variable only during the. periods of division. In the condi- 

 tion of rest its structure * * * js monotonous. 



"The function of the nucleus can only be such an one as is entirely 

 independent of the diflt'erentiation of ])rotoplasm [in different species of 

 living forms], such an one, indeed, as is needed by the most diverse pro- 

 toplasmic structures. This function can only be trophic. * * * 



"Whether this trophic or directive function relates to the metabolic 

 processes, to the formation of centers, or to the regulation of difi'usion- 

 strea/ms of protoplasm, must remain undecided, as much as the proba- 

 bilities are in favor of the latter. 



"The essential nature of the structure of the nucleus is difficult to 

 make out; the fundamental form seems to be a radial one, and in such 

 cases may usually be referred to a radial structure, which is not directly 

 manifest externally. 



S. Mis. 40 30 



