ON THE INFLUENCE OP LIGHT ON THE GROWTH OF PLANTS. 29 



that the skin participates in the respiratory functions, as in Eolis and other 

 of the TritoniadcR. 



These are some of the principal deviations from the normal character of 

 the order, which have induced M. de Quatrefages to detach the genus Eolis 

 and its allies from the order Nudibranchiata, and to place them in his new- 

 order Phlebenterata, in which they are associated with some Mollusca of very 

 inferior organization, containing the genus Acteon of Oken (of which the 

 Aplysia viridis, Mont, is the type), and some other genera still more simply 

 organized. The point of agreement between these is stated to be the pre- 

 sence of a gastro-vascular system, but in the latter genera, which are united 

 into a suborder (^Dermobranchiata), this system appears to perform the three 

 functions of digestion, circulation and respiration, which, indeed, is stated by 

 M. de Quatrefages to constitute the dominant character of the order Phle- 

 benterata. We think, however, that no satisfactory evidence lias been adduced 

 of such union of functions in any of the Nudibranchiata, and so far as we 

 have examined the species our experience is against the supposition. 



The senses are as highly developed in the Nudibi-anchiata as in any of the 

 other gasteropodous Mollusks. The eye is furnished with a well-formed 

 pigment-cup, a spherical lens, a cornea, and a general capsule. It is present 

 in all the genera, but in Doris it can only be seen externally in young indi- 

 viduals; the thickening of the cloak obscuring it in the adult animals, and 

 probably impeding the function. The auditory apparatus is composed of a 

 small vesicle, containing concrete vibratile bodies. Touch is perceived by 

 the whole surface of the body, but is most likely specialized in the labial 

 tentacles, and taste may be inferred from the fleshy lining of the mouth. In 

 a paper read before the last meeting of this Association, we gave reasons for 

 supposing that the sense of smell resides in the dorsal tentacles. These 

 organs have a much more elaborate structure in the Nudibranchiata than in 

 any of the other Gasteropods, and approach so nearly in their lamellated 

 structure to the olfactory apparatus of fishes, that we entertain little doubt of 

 their performing the same function. The sense of smelling is therefore 

 probably enjoyed by them in a higher degree than in any other of the Gas- 

 teropoda. 



In both the great divisions of the order the senses are equally well deve- 

 loped, and we should instance this fact as a reason for keeping them united. 

 In both the nervous systems are the same, as are also the generative organs ; 

 and in both too there is a considerable similarity in the respiratory organs, and 

 perhaps when the circulatory sji-stems are better understood, less deviation 

 will be found to exist in them than is at present supposed. The relationship 

 between the two divisions is also seen in the similarity of the spawn, and, 

 what is still more striking, in the perfect similarity that exists in the larva 

 state of each, and the consequent metamorphosis that both must undergo. 



For these reasons we are disposed to adhere at present to the arrangement 

 of Cuvier, though, from the discoveries that have been recently made in their 

 anatomy, some alterations become necessary in the divisions of the order. 



Researches on the Influence of Light on the Germination of Seeds and 

 the Growth of Plants. By Robert Hunt, Secretary to the Royal 

 Cornwall Polytechnic Society. 



In the course of these investigations many very curious, and in some cases 

 apparently anomalous results have presented themselves, and tended greatly 

 to increase the difficulties of the question. Experiments have been con- 



