148 



the Opalina is allowed to die in water, a cavity forming then 

 between it and the layer of granules belonging to the deeper 

 part of the cortical substance ; which^ as remarked above, 

 might be mistaken for a normal structure, and I think has 

 been by Schultze and Stein in other species. With a good 

 one eighth a very definite structure is revealed in the nucleus 

 after treatment with dilute acetic acid. Minute round nuclei 

 are embedded in its substance exactly as has been so often 

 figured and described in the nucleus of many Infusoria. In 

 the face of this structure it is difficult to understand how the 

 Opalinse can be refused a place among Infusoria proper, or 

 supposed to be stages in the development of worms. 



The cuticle is sharply ridged in this species of Opalina, 

 as in other true Opalinee, which is not the case in the so- 

 called Bursaria Ranee. 



The Opalina infesting Clitellio arenarius is not unlike 

 the one from Nais serpentina, but it is much longer. I have 

 observed that from Clitellio in the Isle of Man. Claparede 

 has found it also, and termed it Opalina jHum. The anterior 

 extremity presents a broad emarginate area, which is not 

 seen in O. Naidos, nor in the very long specimens of O. Naidos 

 which I once found in Lumbriculus at Hampstead. 



Perhaps the most interesting form of Opalina is that named 

 0. jn'olifera by Claparede, observed by him in a small oligo- 

 chset. This form was seen by him reproducing by transverse 

 fission, but in such a way that several pai^tially separated buds 

 remained attached in a chain. In fact, we have here a 

 chain of imperfect zooids, forming a segmented organism, 

 exactly as a segmented worm is formed. 



Pachydermon. — In fig. 10 is draAvn a structure which I 

 found in the spermatic reservoirs of a new species of liimno- 

 drilus, a genus of Oligocha^ts allied to Tubifex, and established 

 by Professor Claparede. I found three of these curious 

 structures in each reservoir of a Limnodrilus which had 

 recently undergone copulation, as was indicated by the con- 

 dition of its copulatory organs ; whilst in those which had 

 not copulated I never found them. 



If this is a distinct parasitic organism it evidently belongs 

 to the genus Pachydermon of M. Claparede, two species of 

 which he has described in his ' Recherches sur les Oligo- 

 chetcs,' from two specimens of the genus Clitellio (Oligo- 

 chaeta). It is also clearly identical with the appearance 

 figured and described by the late M. Jules d'Udekem from 

 the spermatic reservoirs of Tubifex ; but 1 most assuredly 

 cannot regard any one of these structures as indicating an 

 Opalinoid, as does M. Claparede, for whose ojjinion I would, 



