IJFE-CYCLE OF '' OYSTOBIA " IRREGULARIS (mINCH.). 81 



in very j-oung parasites there are noue, and the karyosome 

 appears homogeneous. 



The nucleus of Diplocystis schneideri differs from 

 that of D. minor (and also of Cystobia) in possessing, 

 usually, several karyosomes (figs. 22 and 2G) of various sizes 

 and of the usual vacuolated structure. The nucleoplasm 

 here, as in Cystobia, is in the form of a chromatic network, 

 not, however, so deeply staining. Sometimes it does not 

 appear to be of the same character throughout, a certain por- 

 tion, in which all the karyosomes are imbedded, being denser, 

 more granular, and with a stronger affinity for the chromatic 

 stain (,?, fig. 26).^ 



(c) Formation and probable function of the 

 karyosome. 



In the tiny specimens seen in figs. 30—32 the karyosome is 

 evidently in process of formation. In all three cases it is in 

 contact at one side with the nuclear membrane, and much 

 paler in colour than the chromatin, which is here in the form 

 of deeply-staining grains and lumps in the nucleoplasm. 

 Hence it is most likely that at this time it consists only of 

 the plastinoid portion (of extra-nuclear origin ?) forming a 

 kind of basis, to which will be added later some of the chro- 

 matin fragments, the remainder contributing to the reticulum. 

 In fig. 30 each karyosome is drawn out and elongated in 

 shape, and projects inwards into the midst of the cluster of 

 chromatin grains, many of which probably come into relation 

 with it. As the karyosome increases in size, fluid (?) vacuoles 

 are formed in it, whose contents stain slightly, and these are, 

 as it were, imbedded in the less fluid, darkly stained, chro- 

 matic ground-substance. Different degrees in this vacuo- 

 lisation are seen in the nuclei figured in fig. 33, Pi. 2, which 

 were drawn whole from a preparation stained with picro- 

 carmine. 



' A somewhat similar differentiation of tlie nucleoplasm, in the form of a 

 zone or halo around the karyosome, is described by Berndt (loc. cit.) in the 

 nucleus of G r e e; a r i n a c u n e a t, a. 



