CRUSTACEA. 173 



only existing genus from which we may derive an insight into the 

 organisation of the extinct Trilobitic Crustaceans. This considera- 

 tion has induced me to select for the exercise of the peculiar skill of 

 Mr. Goadby, our anatomical assistant, the well preserved specimens 

 of Liniulus for which the College is indebted to Mr. Boott of Boston, 

 U. S. In these beautiful dissections by Mr. Goadby, the details of 

 the nervous system are clearly displayed, and will, with the rest of 

 the Anatomy of the Limulus, be published by the Council of the 

 College. 



Three principal divisions of the nervous system of the Ci'ustacea may 

 be defined according to the views which I entertain of their functions. 

 Thus, admitting, from analogy, that the supra-cesophageal ganglionic 

 centre {figs. 89. and 90. c) is that in which true sensation and volition 

 reside, then those nervous filaments which are exclusively connected 

 therewith, and some of which would seem to extend the whole length 

 of the animal along the dorsal aspect of the ganglionic columns, would 

 form with their ganglionic centre the true sensori-volitional system ; 

 whilst any other ganglions superadded to the abdominal columns, 

 with the nervous filaments terminating in or originating from them, 

 would constitute the system for the automatic reception and reflection 

 of stimuli. The stomato-gastric nerves, connected partly with the 

 brain and partly with the oesophageal columns, will form a third 

 system analogous to the great sympathetic or organic nerves of the 

 Vertebrata. In these views I coincide with the ingenious physiologist, 

 Dr. Carpenter, and shall feel happy if their accuracy and soundness 

 have received any additional proof from the facts of Comparative 

 Anatomy, which, in the Hunterian Lectures of 1842, were for the 

 first time brought to bear upon this interesting problem. 



The sense of touch can be but very feebly exercised by the com- 

 mon integument of the Crustacea, can hardly, indeed, exist except in 

 those parts of the surface of the body which remains soft and un- 

 defended by the hard crust, such as the joints of the under part of 

 the body, and the surface of the soft tail in the hermit crabs. The 

 fine hairs which project from many parts of the integument may 

 compensate for its low endowment of the tactile sense : the two pairs 

 of jointed antennae {fiff- 90. a) are instruments fitted for the most 

 delicate exploration ; and the smaller but similar organs attached 

 to the jaws, and called palpi, may also receive some impressions 

 analogous to those of savour or smell. The Crustacea have no true 

 tongue, but the sensations of the membrane lining the interior of 

 the mouth and the oesophagus may guide them in the selection which 

 they make of objects of food. 



The sense of hearing is referred to a cavity with a round orifice 



