236 Miscellaneous. 



anomalous Apus-like crustacean, with its dorsal surface presented to 

 view. Subsequent examination of the specimens kindly lent by 

 Mr. Cooper enabled the author to take a different and more probable 

 view of the structural relations of these interesting fossils. Prof. 

 Huxley pointed out that the Pygocephalus Cooperi has some peculiar 

 relations with the little Mysis or Opossum-shrimp, especially in the 

 schizopodous character of its thoracic appendages, in the proportional 

 size of the carapace, and in the gradual increase in width, from 

 before backwards, of the sterna of the thoracic somites. In the 

 proportions of its abdomen, however, the Py^oc(?pAa/M5 approximates 

 more nearly to the true Stomapoda ; and a Gonodactylus bent upon 

 itself presents an appearance in some respects very analogous to that 

 of the fossils in question. 



MISCELLANEOUS. 



On the Nervous System q/Dentalium entalis. -- '* 



By M. T. DE Lacaze Duthiers. ^ 



Three pairs of ganglia constitute the nervous system of animal life. 

 One is placed in the cavity of the foot, another above the mouth, and 

 the third a little in front and on each side of the anus. 



The ganglia of the first pair, or pedal ganglia, are pyriform and 

 approximated ; they furnish the nerves of the foot and a single thread 

 to the diaphragm which separates the visceral cavity from that of the 

 foot. 



The supra-oesophageal ganglia are well developed and approximated 

 by their margins ; each of them presents behind a secondary inflation, 

 which cannot be regarded as another ganglion ; from them arise im- 

 portant nerves, some of which, to the number of five, pass to all the 

 anterior part of the tube of the mantle, others to the mouth, whilst 

 the last, two in number, are distributed in the fold which serves as 

 the base of the tentacular filaments surrounding the base of the buccal 

 process. 



The ganglia of the third pair are small, triangular, distant, and 

 placed on each side a little in front of the orifice of the digestive tube. 

 They only give origin to a long nerve, which after gliding between 

 the elements of the liver, passes to the dorsal surface to run to the 

 posterior extremity of the body, to the cavity through which the 

 water serving for respiration enters. From their position and the 

 nerves which originate from them, these ganglia appear to be exactly 

 analogous to the branchial ganglia of the lamellibranchiate Acepha- 

 lous Mollusca. 



Connective nerves and commissures unite these little nervous 

 centres amongst themselves. The cords which unite the pedal to the 

 supra-CESophageal ganglia enclose the first portion of the digestive tube 

 in a collar and are deeply seated ; those which join the supra-oeso- 

 phageal to the posterior ganglia are in the fold of union of the mantle 



