CBU8TACEA OF NEW ZEALAND, 205 



i 



time with very little food ; thus Dr. John Stoan states that a blind fish (Ambli/oj]s/s 



spelcBus) lived for twenty months " without having taken any visible food " (see Packard 

 [83, p. 127]). 



Arrested Development. 



The fauna of caves and underground regions presents us with several examples of 

 what appears to be an arrest of development. 



Packard has drawn attention to one example. Writing of the cave-dwelling Myriopod 

 Pseudotremia cavernarum, and comparing it with the widely diffused Li/siopetalum 

 lactarium, Say, he remarks : — " It differs in having only about half as many segments as 

 in its out-of-door parent form (this diminution in the number of segments being due to 

 arrest of development) . . ." [83, p. 120]. 



In our New-Zealand forms we have a good example of the same thing in Cruregens 

 fontanus, which has the seventh segment of the peraeon small and without appendages, 

 as is the case in the young forms of many Isopods. It seems tolerably clear that we have 

 here simply a case of arrested growth, and not a reversion to a true ancestral form, for 

 while in the process of development of the embryo of the Isopoda the seventh pair of the 

 appendages of the perseon are the last to be developed, I am not aware of any reason for 

 supposing that the ancestors of the Isopoda ever j^ossessed only six pairs of appendages 

 to the perseon. 



In remarking on this example, Alois Humbert quotes other cases observed by Heller. 

 He states (Archives des Sciences naturelles, viii. [Sept. 1882] p. 267) :— 



" Nous rapj)ellerons a ce sujet que le Dr. Camil Heller a d^crit un genre cavernieole 

 de Glomeride (Trachysplicera), se distinguant des Glomerls en ce qu'il ne possede que 

 11 segments au lieu de 12, et 15 paires de pattes au lieu de 17 ; le menie auteur a fait 

 connaitre un autre Myriapode [Brachi/desmus) provenant, comme le precedent, des grottes 

 de la Carniole et ne differant des Polydesmus que parce qu'il n'a que 19 segments au 

 lieu de 20, nombre normal cliez les Polydesmides adultes. Si les TrachyspJuera Schmidt'd 

 et Brachydesnms subterraneus ont 6te etablis d'apres des individus reellement adultes, 

 ce qvie nous avons certaines raisons de croire, il y aurait chez ces deux Myriapodes un 

 arret de developpement tout-a-fait semblable a celui que M. Cliilton vient d'observer aux 

 antipodes chez son Crustace souterrain." 



M. Humbert attributes this ai'rest of development in cave-animals to the influence of 

 darkness, the lack of sufficient food, and the other necessary conditions of their environ- 

 ment. 



I have given above merely the examples of arrested development that are known to 

 me ; probably a full examination of the literature of the subject would show that many 

 others have been recorded. 



Habits. 



In their habits in confinement the subterranean Crustacea seem to differ ])ut little from 

 their surface allies. Observations on their habits have been made by Hogan [59 and 60], 

 Stebbing [108], Packard [83, pp. 123-130, &c.], and others. According to Hogan, 



