6 INVERTEBRATE MORPHOLOGY. 



nuclear activity seems to disappear, a new one subsequently 

 forming. Traversing the space enclosed by the membrane, 

 so as to form a network, are fibres which do not stain very 

 deeply with the usual staining fluids and which are composed 

 of a substance termed limn, which does not, however, appear 

 to differ essentially from the plastin of the cytoplasm. In- 

 deed it is not improbable that the linin network is con- 

 tinuous through the nuclear membrane with the plastin 

 reticulum and that both are identical, as is also the caryo- 

 lymph contained in the meshes of the linin with the cyto- 

 lyinph. 



A more characteristic substance is the chromatin (Fig. 

 1, cr), so called from the strong affinities it shows for many 

 staining fluids, such as carmine, hieinatoxylin solutions, and 

 certain aniline stains. It seems to consist of the substance 

 nuclein, already alluded to, and in the resting nucleus forms 

 a reticulum intimately associated with the linin network, 

 which it usually to a considerable extent obscures. Where 

 the various strands of the network meet, thickenings of the 

 chromatin sometimes occur, producing densely staining 

 'bodies (nl) to which the term uucleoli is given, though it is 

 probable that bodies of a somewhat different composition 

 are also included under this name ; for there are usually to 

 be found in the nucleus, imbedded in the substance of the 

 network, one or more spherical bodies whose chemical re- 

 actions differ noticeably from those of the chromatin nucleoli, 

 the substance of which they are composed being termed 

 paranuclein or pyrenin. 



There are then in the cell the following structural con- 

 stituents : 



( membrane (cell-wall), 

 I. C} r toplasm : -/ reticulum (plastin), 

 ( caryolymph. 



membrane, 

 reticulum (limn), 

 II. Caryoplasm : ^ caryolymph, 



| chromatin network (nuclein), 

 nucleoli (nuclein and parauucleiu). 



