NUCLEI OF MUSCLE-FIBRE IN NECTURUS LATERALIS. 465 



the case of the few isolated, however, I could make out a cer- 

 tain amount of transverse striation of the membrane. 



Further, as to the transverse furrows being often at acute 

 angles with one another, an explanation for this may be found 

 in the facts now to be described. 



A few nuclei presented other appearances than those men- 

 tioned (fig. A, 9, 15, 16, 18, 19). Here the form of a oblong- 

 meshed reticulum like that of the muscle-fibre was observed 

 and considered by me at first to be caused by an impression pro- 

 duced by the latter on the surface of the nuclear membrane. I 

 found, however, in cases where it could admit of no doubt, that 

 the reticulum was not on, but within the nucleus. In other 

 words, there is in the interior of some nuclei a 

 reticulum like in every respect to that found in 

 the muscle-substance. In these cases no chromatine or 

 caryoplasma could be observed. 



On the other hand, I observed a few nuclei in which the 

 caryoplasma was approximately square meshed (fig. a, 23). The 

 quadrangular form of the meshes is exhibited oftener and better 

 in the nuclei from the heart muscle (fig. a, 20, 21). This form 

 of the reticulum appears to be one of the stages transitional 

 between the reticulum of the young nucleus and that referred 

 to in the last paragraph. 



In view of these facts it is safe to infer, as Carnoy and 

 Melland have done, that the muscle reticulum is simply the 

 modified cytoplasma, the caryoplasma being derived from the 

 latter.^ 



Nuclei with such a modified caryoplasma as represented in 

 fig. A, 20 and 21, must be capable of movement, or contraction 

 and extension. This movement has been observed in the nuclei 

 of vegetable cells by Hanstein,^ and in the nuclei of white blood- 

 corpuscles of Necturus by Gage,^ and is amoeboid in character. 

 But the possession of a square-meshed reticulum implies exten- 

 sion and contraction in definite directions — the nucleus con- 



' See Carnoy, op. cit., p. 250. 

 - ' Hot. Zeit.,' 1872, p. 22. 

 3 ' Science,' Jan. 8th, 1886. 



