OBSERVATIONS ON STRUCTURE OF CELLS ANT) NUCLEI. 333 



usually loDgitudinally. In such a nucleus we notice that this 

 intranuclear network forms two distinct groups — one for each 

 ])art of the nucleus — connected with each other hy parallel 

 threads. There are nuclei possessed of one or two smaller 

 or larger rounded buds; these contain a small network con- 

 nected with the bulk of the intranuclear network by a few 

 small threads. This is shown in b, of the accompanying 

 woodcut. 



It is probable, from this, that the division and multiplica- 

 tion of the nucleus of unstriped muscle-fibres is ])receded 

 by a process of gemmation. In most muscle-fibres the 

 nucleus is seen in profile, and the bulk of the intranuclear 

 network occupies an axial position ; from it pass numerous 

 transverse fibrils towards the sides of the nucleus. 



In all muscle-fibres the intranuclear fibrils may be traced 

 to emerge as a bundle from the pole of the 7iucleus, and to 

 become identified with the bundle of fibrils representing 

 the core of the muscle-fibre itself. This point, viz. the con- 

 nection of the intranuclear network with the bundle of 

 fibrils of the muscular substance is shown well enough in 

 preparations stained with hematoxylin, but it is perhaps 

 still better shown in parts of mesentery stained first with 

 [)icrocarmine and then with heematoxylin. In a muscle- 

 fibre which, close to the nucleus, divides into two processes 

 like the one represented in fig. 17, c, we observe that the 

 intranuclear network sends forth two bundles of fibrils, 

 one for each division. 



A very interesting relation that I have been able to ascer- 

 tain in some nuclei, is this : the nucleus possesses a 

 small circular opening at each pole, through which the bundle 

 of fibrils emerges. (I have tried to represent this in fig. 

 17, d, but fear not with great success). The same relation 

 probably exists in all fibres. 



Thus, we may regard the unstriped muscle-fibre as corn- 

 posed of a sheath with annular thickenings, and a bundle 

 of delicate fibrils which at one more or less central point 

 forms a delicate network; this surrounded by a special 

 membrane — except where the network is in connection with 

 the bundle of fibrils — represent the nucleus. 



I am unable to say what the nature of that sheath is, 

 but I think it is probably of the nature of an elastic 

 sheath, and I can well understand its importance in the 

 function of the muscle-fibre. The central bundle of fibrils 

 having its fixed point, as it were, in the intranuclear network, 

 shortens during contraction towards this, and is brought back 

 again into its condition of rest by the elasticity of the sheath. 



