406 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



cytoplasm results in less movement of the latter during fixation and therefore 

 less disturbance in the form of the nucleus. 



The existence of a distinct nucleai- membrane has been frequently accepted as 

 incompatible with the discharge of sphervdes as such from the nucleus into the 

 cytoplasm, and the partial or complete disappearance of this membrane has been 

 interpreted as indicating an increased reaction between the nucleus and the cyto- 

 plasm. As Professor Chubb's conclusions for Avtedon assume the discharge of 

 formed spherules into the cytoplasm, though a distinct nuclear membrane be 

 present, and as his interpretation of the cell processes takes no note of the con- 

 dition of the nuclear membrane, he finds it necessary to offer some explanation of 

 the latter structure which shall not necessitate the assumption that the existence of 

 a clearly defined nuclear membrane in any way interferes with an active reaction 

 between the nucleus and the cytoplasm, or that it possesses in the living egg the 

 firm consistency which it often appears to possess in fixed material. 



The nuclear membrane is always present in the oocyte of Antedon. Only 

 when the nucleus is very irregular in form does the nuclear membrane appear 

 to be interrupted. The partial disappearance of the limiting membrane in these 

 nuclei is, however, always directly associated with the irregularities in the nuclear 

 outline and is, according to the belief of Professor Chubb, due to the nuclear 

 membrane of these points being cut in a very oblique direction, a natural result of 

 the wrinkled form of the nucleus. This suggestion receives considerable support 

 from the appeai'ance of tangential sections of the nucleus, in which it can be 

 readily seen that the nuclear membrane is perfectly well marked on any part of 

 the nuclear outline which does not quickly change its position in neighboring 

 sections of the series, but is invisible in those regions of the outline which do 

 quickly alter their position in adjacent sections, and which thus show that they 

 are cut extremely obliquely. The frequency with which this local disappearance 

 of the nuclear membrane has been described as associated with nuclear irregu- 

 larity suggests that the above explanation will be found to apply to these other 

 cases also. 



Although we may therefore assume that the nuclear membrane is always 

 present at all stages of the oocyte's growth, it nevertheless varies greatly in 

 appearance according to the nature of the fixing reagent employed. It is, for 

 example, always difficult to see after the use of sublimate, while in Hermann 

 material, and indeed after the use of all reagents containing a free acid, it is 

 not only quite distinct, but usually deeply stained. It is tlius seen that the 

 behavior of the nuclear membrane shows a striking parallelism with that already 

 described for the cytoplasm. Those reagents which give a well-fixed cytoplasmic 

 reticulum give also a distinct nuclear membrane, while those reagents, such as 

 sublimate, after the use of which the cytoplasmic reticulum is absent or masked 

 by the metaplastic substances, give a nuclear membrane which is indistinct and 

 often difficult to detect. When there is a distinct cytoplasmic reticulum, as for 

 instance, after the use of Hermann's fluid, the nuclear membrane appears to be 

 continuous with the strands of the latter. Professor Chubb thinks that this 

 behavior indicates that the nuclear membrane consists of a layer of the living 



