﻿178 Proceedings of the Royal Physical Society. 



larger spherical forms may have a diameter of 100 />t or even 

 more. The protoplasm varies slightly in character. It 

 is in many individuals very finely and evenly granular 

 throughout its whole extent, showing no differentiation 

 into ectoplasm and endoplasm, and is quite free from 

 vacuoles or other inclusions (Fig. 2). In other cases it 

 may be more or less vacuolated towards the centre, or 

 may show a slightly coarser granulation ; occasionally 

 refractive inclusions may be present which stain with 

 eosine and also with thionin. These last are, however, 

 not very frequently met with. Sometimes there may be 

 a ring of protoplasm towards the centre which takes the 

 stain a little more deeply than the rest of the protoplasmic 

 body, and occasionally the nuclei are grouped to a certain 

 extent within the ring. I do not think that this appearance 

 has any particular significance. 



The numerous nuclei are of a type which is widespread 

 amongst the Protozoa, but more usually found in flagellates 

 than in other forms. It is characterised by the presence of 

 a relatively large central karyosome — the " Binnenkorper " of 

 Senn — surrounded by a fine sharply marked membrane, which 

 takes up the chromatic stains to a certain extent; the 

 intervening space between the karyosome and the membrane 

 being traversed by fine staining threads which radiate out 

 from the karyosome. This nucleus might be represented as 

 a bubble containing a small sphere, with radial strands 

 passing from the sphere to the wall of the bubble (Figs. 2, 3, 

 etc.). That the nucleus is spherical and not wheel-shaped, 

 as, for instance, that of some trypanosomes, is quite obvious 

 from the fact that the same appearance is always presented, 

 no matter from what aspect the nucleus is observed. The 

 karyosome of the nuclei in Icthyosporidium is in the resting- 

 stage very homogeneous and compact in its appearance, and, 

 except for the small size, is identical with that of many 

 free-living flagellates. The fine rays just described have 

 not been observed in Icthyosporidium gasterophilum nor in 

 other members of the order of the Haplosporidia, although 

 nuclei identical in all other respects are not uncommon in 

 the group. These rays are, however, absolutely constant 



