1890.] and the size and number of their sense-organs. 97 



by this reduction. It has been assumed by many that this benefit 

 must be so marked as to lead to the Natural Selection of the 

 individuals thus varying. This principle has been invoked especi- 

 ally in the case of sense-organs, and, for example, it has been 

 suggested that the blindness of cave-fauna may have come about 

 by its operation. 



With the object of testing the truth of this assumption, it 

 seemed desirable to obtain a knowledge of the normal variations 

 in size and number of sense-organs occurring within the limits of 

 a single species. The cases chosen were (1) The olfactory organ 

 of Fishes (Eel, Loach, Pleuronectidce, &c), and (2) The eyes of 

 Pecten opercularis. In the first case tables were given shewing 

 that large individual fluctuations occur, but that on the whole the 

 number of olfactory plates, increases with the size of the body. 

 It was pointed out that the size of the eye in Fishes also increases 

 with the size of the body. 



In the case of Pecten, however, though the size of the eyes 

 increases with the diameter of the animal, yet in specimens having 

 a diameter of 3 cm. — 6 cm. the number of the eyes is not thus 

 related (cp. Patten), but varies in a most surprising and, as it 

 were, uncontrolled manner. 



Statistics were given shewing that in individuals of the same 

 size, the number of eyes may vary between 70 and 100, and that 

 no uniformity is to be found. It was pointed out that these eyes 

 are large and complicated organs, having lens, retina, tapetum, 

 &c, involving great cost in their production. These facts suggest 

 that the " economy of growth " cannot be a principle of such 

 precise and rigid character as to warrant its employment as a basis 

 for speculation as to the mode of evolution of a species. The 

 diverse results in the case of the two sets of organs examined 

 further indicate that the problem is one of far greater complexity 

 and shews clearly that argument from analogy is inadmissible in 

 these cases. 



(4) On the Oviposition of Agelena labyrinthica. By C. War- 

 burton, B.A., Christ's College. 



[Abstract; reprinted from the Cambridge University Reporter, Nov. 18, 1890.] 



The oviposition and cocooning of Agelena labyrinthica is a 

 striking case of the performance of a series of complicated opera- 

 tions in obedience to a blind instinct. 



The eggs are always laid at night, but the presence of artificial 

 light is quite disregarded by the animal. 



For about 24 hours before laying, the spider is engaged in 

 preparing a chamber for the purpose. 



