CETJSTACEA OF NEW ZEALAND. 261 



of the North-American caA es, in which all stages of degeneration are met with, thus 

 sums up the effects of the loss of sight on the eyes and optic lobes : — 



"1. Total atrophy of optic lobes and optic nerves, with or without the persistence in 

 part of the pigment or retina and the crystalline lens {CcBcidotma, Crangonyx, Chthonius, 

 Adelops, Pseudotremia). 



" 2. Persistence of the optic lobes and optic nerves, but total atrophy of the rods and 

 cones, retina (pigment), and facets [Oronectes). 



"3. Total atrophy of the optic lobes, optic nerves, and all the optic elements, 

 including rods and cones, retina (pigment), and facets {Anophthalmus, Scotei'pes, and 

 ?Anthrobia)" [83, p. 118]. 



He also points out that we never find any rudiments of the optic lobes and optic 

 nerves ; if they are wanting at all they are totally abolished ; while, " on the other hand, 

 we have series, as in CcecidoicBa or Chthonius, where there is but a single, or two or 

 three, or several crystalline lenses, partially enveloped in pigment " [83, p. 118]. He 

 lays stress on these facts as opposed to what he calls the " invariably slow action involved 

 in pure Darwinism." 



Many conflicting statements have been made by different authors as to the presence 

 or absence of the eyes of the European species Niphargus puteanus, and in consequence 

 it was fuUy investigated by Leydig, who found " that the optic ganglion is present, but 

 not the eye, though pigment-spots mimicking the eye have led some observers to believe 

 that an eye existed in fact " [quoted from Stebbing, 108, p. 481]. 



WhUe this may no doubt be quite true of the specimens observed by Leydig, it 

 appears from Packard's results that the external eye may be represented in varying 

 degrees of completeness in different specimens of the same species ; and that being so, 

 there is no ground for refusing to believe that it may be altogether absent in some, 

 though present (more or less imperfectly) in others. Forel, too, has pointed out that the 

 blindness of Asellus Forelii, Blanc, is not without exception ; two specimens taken near 

 Morges and Ouchy, at depths of 200 m. and 300 m., presented rudiments of eyes, whilst 

 all other specimens taken up to that time — even young taken from the brood-pouch of 

 the female — were absolutely devoid of eyes [40, p. 114]. We can hardly suppose that 

 Forel was deceived by mimicking pigment-spots in these two specimens only. 



In the New Zealand subterranean Crustacea I have not been able to find any external 

 trace of eyes except in the one species Crangonyx compactus, in which the eye is repre- 

 sented by two or three imperfect lenses apparently quite without pigment. In all the other 

 species all trace of external eyes appears to be wanting. I regret that as yet I have had 

 no opportunity of making sections to study the condition of the optic lobes and nerves. 



Compensation for Loss of Eyesight. 



Several authors have pointed out that in many species inhabiting the dark regions of 

 caves or underground waters the loss of eyesight has been more or less compensated 

 for by increased powers in the other senses — especially those of touch and smeli. Many 

 of the species are more slender and possess longer antennaj, legs, and other appendages 



34* 



