414 Messrs. Alder and Hancock on a proposed New Order 



Further than this we have not been able to make out the vascular 

 system. 



When subjected to the pressure of the instrument, the pulsa- 

 tions of the heart are very slow, but when the animal is at liberty 

 it beats with great rapidity, — probably ninety times or even more 

 per minute. We could not ascertain the number exactly on account 

 of the restlessness of the little creature, and the impossibility of 

 seeing the pulsations excepting in some particular lights. 



M. de Quatrefages describes his Chalidis carulea to be without 

 a heart or any traces of a vascular system. We have seen that 

 Limapontia nigra possesses not only a well-formed bipartite heart, 

 but that it has also an arterial system, and from the sudden con- 

 traction of the auricle behind it, it is evident that the venous 

 system is not altogether deficient, or that portion of it, at least, 

 which M. Milne-Edwards calls branchio-cardiac. The deductions 

 of M. de Quatrefages therefore, in this instance, cannot be sus- 

 tained. 



Respiration appears to be performed by the whole surface of 

 the body, as it is entirely clothed with vibratile cilia, not even 

 excepting the under surface of the foot*. The cilia are large and 

 vigorous, and their action may be detected under favourable cir- 

 cumstances with a powerful single lens. 



Nervous System and the Senses. — We have not paid sufficient 

 attention to this part of the subject to enable us to give a detailed 

 account of its anatomy. The cerebral ganglia were consequently 

 not fully determined : they are placed as usual round the com- 

 mencement of the oesophagus, and are four or more in number. 

 The central or upper pair are somewhat pyriform, and are placed 

 further apart than usual : they are connected by a stout com- 

 missure. The lateral pair are rather smaller than the central 

 ones, and are of an elliptical form : they appear to be united below 

 the oesophagus by a short collar and two small oval buccal 

 ganglia ; but these were not determined with sufficient certainty. 

 Nerves pass from these central ganglia to all parts of the body. 



The optic nerve is of considerable length, and springs from the 

 outer margin of the central ganglion, where it joins with the lateral 

 one. This nerve enters the base of the black pigment cup of the 

 eye, which is large and pretty regularly formed. Half-buried 

 within the mouth of this cup is a spherical crystalline lens, 

 which is protected in front by a cornea, that passes close in ad- 

 vance of it : the whole is enveloped in a thin membranous sac. 



* Limapontia is not, by any means, the only slug that has the under sur- 

 face of the foot ciliated. We have detected these minute organs on the same 

 part in the Nudibranchs, and in Purpura, Littorina and Patella. It is there- 

 fore probable that all the Gasteropods have cilia on the crawling disc. 



