1890.] upon, the Fresh-water Crayfish. 77 



for a mouth or two if not permanently. Broadly speaking those 

 actions which may be considered voluntary are the most interfered 

 with by nicotin. 



Further, a comparison of the effects of nicotin on the crayfish 

 and of the effects of section of different parts of the central nervous 

 strand, such as those made by Ward, makes it probable that in each 

 ganglion there is a part which is paralysed by nicotin, and a part 

 which is only slightly affected; the former being concerned with 

 the more complicated movements, the latter with the simplest 

 kind of reflex action. 



On account of the lasting action of nicotin on certain functions 

 of the ganglia, i.e. probably on certain nerve-cells, it is not unlikely 

 that a morphological change may be visible in some of the nerve- 

 cells of each ganglion, if the ganglia be observed some time after 

 nicotin has been given. But as this point requires a careful study 

 of the normal structure of the ganglia of the crayfish, I reserve it 

 for a later communication. 



Electrical stimulation of the nervous chain in a crayfish a short 

 time after nicotin has been given to it differs in its effect from that 

 produced in a normal crayfish; the contraction is less, and is limited 

 to one or two segments above and below the point of stimula- 

 tion ; apparently each ganglion sends fibres to two or three seg- 

 ments, and the effects observed are due to a stimulation of these 

 nerve-fibres after they have left the ganglion ; whereas the other 

 ascending and descending nerve-fibres end in nerve-cells in the 

 various ganglia; where in consequence of the action of nicotin, 

 the nervous impulse set up in the fibres is stopped. 



(2) On a new species of Phymosoma. By Akthtjr E. Shipley, 

 M.A., Christ's College. 



During a visit to the Bahama Islands, Mr Weldon was fortu- 

 nate enough to find three specimens of a large brown Phymosoma, 

 whilst investigating the Fauna of the Bimini lagoon. He came to 

 the conclusion that these specimens belonged to no described 

 species of Phymosoma, and was good enough to hand them over 

 to me for description. I propose to call this species Phymosoma 

 Weldonii. 



The length of the three specimens varied between 3'5 cm. 

 and 3 cm. ; their bodies are plump and slightly curved. The 

 ground colour of the preserved specimens is light yellow, but this 

 is modified over the surface of the body by dark brown papillae. 

 In all three specimens the introvert is retracted, and in this condi- 

 tion is about 1 cm. long. The papillae are of two kinds, flat, brown, 

 rectangular, low elevations on the skin of the trunk, and conical, 

 elevated protuberances of a light colour on the introvert. 



