272 DE. C. CHILTON OF THE SrBTEEEANEAN 



In speaking of the variety freibergensis, Sclineider, of Aselliis aqiiatieus, Monies 



says : — 



" Differents auteurs (Schneider, Chiltou, etc.) attachent beaucoup d'importance a la 

 date a laquelle ont ete fores les pmts dont ils ont etudie les eaux, admettant volontiers, 

 mais bien gratuitement, a notre avis, que c'est a cette epoque que les animaux y sont 

 arrives et ont commence a se modifier. Nous avons deja fait entendre, a propos du 

 Cyclops pulchelhis (p. 34), que cette iagon naive de proceder a I'etude de la variation 

 des especes ne pent se soutenir, car elle ne tient pas compte d'un facteur important 

 dans la question, celle des eaiix souterraiiies, dans lesquelles les animaux observes pou- 

 vaient vivre avant le forage, et par lesquelles, grace aux infiltrations, de nouveaux in- 

 dividus a I'etat d'oeufs, ou meme a I'etat parfait, peuvent arriver a tout instant, comme 

 nous I'avons fait remarquer plus haut (pp. 37, 38) " [78, p. 52, footnote]. 



It is true that in my first paper on the Subterranean Crustacea of New Zealand I did 

 mention the age of the well from which they were obtained, because I wished to give 

 all the facts that might have a bearing on the question, and though the age of the well 

 has, of course, nothing to do with the development of the Subterranean Crustacea, it may 

 have had some efifect on numbers occurring at that particular place ; but there is nothing 

 in my paper that can be interpreted to mean that I imagined that the Crustacea — all 

 true subterranean forms — had begun to modify only after the well was bored ; and in 

 my second paper [23, p. 87, &c.] I made it quite clear that the Crustacea are inhabitants 

 of the underground waters and not merely of the wells. 



The cases brought forward by Schneider, i. e. Gammarus pulex, var. suhterraueus, and 

 Asellus aquaticus, var. frelhercjensis, seem to me to be quite different. Here, as in 

 the case of Gammarus fluviatilis, var. (TEmmerin, mentioned by Moniez himself, we 

 have subterranean varieties which difi'er from the parent species still found on the 

 surface only in a few small points, such as colour, slight degeneration of the eyes, &c., 

 and though 1 do not know what age is to be assigned to the mines in which Schneider 

 found his examples, I see no reason for doubting that these slight difl'erences have been 

 acquired in a very few generations. Other similar examples are given by Packard; one 

 is that of some examples of an isopod found in subterranean regions, which, although 

 of the normal form and size of Asellus communis (the surface species), were bleached 

 as white as Ccecidotea stygia, and of this variety, which he calls iHilUda, Packard 

 remarks : — " It is interesting to note the occurrence of this bleached variety, which may 

 have become thus modified after but a few generations, perhaps but one or two " [83, p. 32]. 



Other examples given appear to confirm this view, and all go to show that sUght 

 modifications, such as m. the cases mentioned above, may be produced mthin very 

 short periods. 



X. Conclusion. 



In the foregoing pages I have endeavoured to give as full and accurate an account 

 of the Subterranean Crustacea of New Zealand as the material and the time at my 

 disposal would allow. But although the work has gradually grown vuider my hands 

 until the present memoir has far exceeded the limits I originally anticipated, its 



