made at Naples in the winter of 1871-72. 



89 



cilia of the "Topfchen" are in no wise peculiar. What he 

 has supposed to be a head or knob on the end of the cilium is 

 really nothing but the bending over of the extremity of the 

 cilium under the influence of the dilute acetic acid which he 

 used. I convinced myself time after time that the cilia of the 

 Topfchen are perfectly normal, by study, with Hartnack's 10 ^ 

 immersion, of living specimens, and of others treated with 

 osmic acid. By the use of acetic acid I obtained the knob-like 

 appearance which deceived Alexander Brandt. 



Further I have found out the source of the " Topfchen." 

 They are to be observed in great numbers attached icithin the 

 curious pair of tubes or vessels formed by duplicatures of the 

 peritoneal membrane, which lie on each side of the oesophagus, 

 and the connexion of which with the tentacle-crown was so 

 well shown by Brandt in his memoir. They develop as " but- 

 tons " on the cellular surface (fig. 3), which is throughout the 

 perivisceral cavity provided in parts with patches of cilia-bear- 

 ing protoplasm ; and then they become detached and swim off 

 into the fluid. The whole history of this beautiful peritoneal 



Fior. 3. 



tissue and its shedding of elements into the perivisceral fluid 

 is of extreme interest ; but I cannot go into it until my draw- 

 ings can be given. So much for the Topfchen at present. 

 Next as to the ova. These occur of all sizes in the perivisceral 

 liquid ; and Brandt appears to have supposed that they take 

 origin in it. Various zoologists have tried to establish this or 

 that structure as the " ovary." Some have assigned this nature 

 to the pair of large brown tubes opening to the exterior, 

 so paradoxical in character. MM. Keferstein and Ehlers 

 mistook the unicellular cutaneous glands and some vagrant ova 



