OBSERVATIONS ON STRIPED AND UNSTRIPED MUSCLE. 97 



The continuity and identity of nuclear and extranuclear 

 networks is strongly supported by Sedgwick's remarkable ob- 

 servations on the early stages of Peripatus. 1 He not only 

 demonstrates the continuity of the extranuclear and intra- 

 nuclear networks, but he also shows that during segmentation 

 of the ovum the cells do not become completely separated, but 

 remain connected by their protoplasmic networks, i.e. that 

 the intracellular networks of all the cells are continuous. 



He also states that the so-called nuclear membrane is reti- 

 cular in nature and not a true membrane, being, in fact, part 

 of the general reticulum of the cell. In the cells described by 

 Sedgwick there is no doubt that the reticulum is the active 

 portion of the cell, for the rest of the cell consists simply of 

 vacuoles. 



Flemming states, 2 as Sedgwick also noticed, that the first 

 change observable in a cell whose nucleus is about to divide 

 is in the extranuclear protoplasm. Strasburger 3 further states 

 that the fibrils which form the nuclear spindle originate in the 

 surrounding "cytoplasm" at the time of division. This ap- 

 pears to be direct evidence of an active function in the intra- 

 cellular network. 



These considerations show that the function of intracellular 

 networks is very probably of an active nature. 



We have now to consider the networks of striped and un- 

 striped muscle. Both these forms of network are non-essential 

 to contraction, for we have seen that many muscle-fibres of 

 invertebrates are devoid of a network of any kind ; but that 

 they modify the nature of the contraction is very probable. 



We have seen that the network of striped muscle is developed 

 when rapid movements are to be performed ; this shows that 

 the function of contraction is intimately associated with the 

 presence of the network. 



The chief points of difference in the contraction of striped 



1 ' Quart. Journ. Micr. Sci.,' vol. xxvi, 1886, pp. 175—212. 

 ' ' Zellsubstanz, Kern u. Zelltheilung,' Leipzig, 1SS2. 

 3 'Arch. i'. Mikr. Anat.,' Bd. xxiii, "Die Controversen der indirecten Kern- 

 theilung." 



VOL. XXVIII, PART 1. NEW SER. G 



