StatoUasts of Fresh-nxtter Pohjzoa. By C. F. Jlousselet. 143 



Dr. S. F. Harmer, F.R.S., who, on the invitation of the President, 

 opened the discussion, said that, in the first place, it might be noted 

 that fresh-water Polyzoa were a very difficult study, because of the great 

 variability which occurred in them. If one collected a number of 

 samples of fresh-water Polyzoa from different localities, great difficulty 

 would be experienced in sorting them into their species. And one 

 thing which had added to the difficulty was the divergence of opinion 

 with regard to their proper nomenclature. In a comparatively recent 

 monograph, Professor Kraepehn, of Hamburg, had, rather gratuitously, 

 added to the complication by summarily throwing overboard all the old 

 names. On the ground that Flumafella repens and certain other names 

 had been used in such a variety of senses that it was almost impossible 

 to know what was meant by them, Kraepelin proposed that they should 

 be rejected in favour of new names of his own. Unfortunately, 

 Dr. Harmer had noticed a tendency on the part of recent writers to 

 adopt the names suggested by Kraepelin, whicli are contrary to all 

 the recognized principles of nomenclature. 



The statoblast is essentially an adaptation to fresh-water, and, as 

 Mr. Rousselet said, is quite unknown in marine representatives of the 

 group. Here and there in literature one found statements to the effect 

 that objects comparable to statoblasts had been discovered in marine 

 Polyzoa. But, so far as he knew, not one of those statements would 

 bear critical examination ; and he thought it might safely be assumed 

 that statoblasts were structures entirely confined to the fresh-water 

 members of the group. Perhaps their nearest analogues were the 

 gemmules of fresh-water sponges. Their object was, in one respect, a 

 very obvious one ; they were (in these latitudes) for the purpose of 

 enabling the organism to get through the winter, and to germinate in the 

 following spring. Physiologically, they bore considerable resemblance 

 to the seeds of flowering plants. One of their great peculiarities, as 

 Mr. Rousselet had said, was that they floated on the surface of the 

 water, and that led to one or two somewhat remarkable results. 



He thought it was true of fresh-water Polyzoa that they were not, as 

 a general rule, found in water which was flowing swiftly, if indeed they 

 were found in such water at all. Anything floating on the surface of 

 the water was liable to be carried down stream, and it would be difficult 

 for a fresh-water Polyzoon to maintain itself in a stream in which the 

 current flowed rapidly in one direction. He might refer to a locality 

 where there was a pond which formed a lateral diverticulum of a river 

 which always flowed in one direction ; and he knew that if he went to 

 that pond in any ordinary summer he could find fresh-water Polyzoa, 

 whereas he did not find any in the river a few yards distant. 



There was another point which had struck the attention of various 

 observers. Statoblasts are liberated in the autumn, and float on the 

 surface of the water, where they remain till the spring, at which season 

 they germinate. They were thus exposed to the rigours of the winter ; 

 and if the water froze, the statoblasts would naturally be included in the 

 ice. This point had been investigated by Braem, "who had published 

 evidence tending to show that the germination of statoblasts was dis- 

 tinctly improved by frost. This is probably not a universal rule about 

 statoblasts ; it was possible for them to germinate without having under- 



