DECAPODA, 



211 



upper interior portion of tlie stalk near the cornea represents the first appearance of the 

 ocular papilla. 



The rostrum is now not much more than one-qviarter the length of the carapace ; 

 dorsally it is armed with from six to eleven teeth ; ventrally it is at first unarmed, teeth 

 however, soon appear in the form of nicks in the thin margin. Tlie blunt dorsal spine 

 near the posterior margin of the carapace is still present, but it is still quite rudimentarv 

 and shortly disappears. The 6th abdominal somite is less than three times the length of 

 the 5th, and more dorso-lateral spines appear on the telson (fig. 24), the terminal spines of 

 which have all disappeared, with the exception of the two large pairs and one small one 

 which has taken up a central position. 



The oral appendages have now assumed a form closely resembling those of the adult, 

 and the first two pairs of pereiopods have, by an outgrowth of the propodus parallel to 

 the dactylus, become possessed of chelae; these, however, in smaller examples are still 

 quite rudimentary. The ischium and merus of the last three pairs bear a few spines on 

 their inferior border, the full complement being formed subsequently. 



The growth of the rostrum and other changes which the parva form undergoes before 

 finally attaining its full dimensions have been adequately treated by Coutiere {loc. cit.). 



The most interesting and remarkable feature of the metamorphoses of A. purpurea is 

 the reduction and subsequent growth of the cornea and rostrum. In the youngest stages 

 the rostrum is long and is gradually reduced in size until a minimum is reached in the 

 " ixirva " foiiii, from thence onwards it grows with each succeeding moult until the adult 

 form is attained. In old specimens the extreme apex frequently appears to be worn 

 down and is thus to some slight extent again reduced. 



The development of the eye is somewhat different ; it shows a gradual growth with an 

 increasing number of facets and is widest across the cornea until the "parva '' form is 

 reached. It is then suddenly diminished in size and the cornea becomes narrower than 

 the eye-stalk ; the number of facets has nevertheless very considerably increased. By 

 subsequent growth the eye at length reaches the adult condition with the cornea once 

 more wider than the stalk. 



All these young specimens were caught between 100 fathoms and the surface, with 

 the exception of the two referable to the post-larval or " parva " form ; these were taken 

 between 750 and 500 and between 500 and 400 fathoms respectively *. 



The frequent occurrence of the larva) of this species in the upper sti*ata of the water 

 and the apparent absence in that horizon of the post-larval forms seem to suggest that 

 at the approach of the "parva " stage the animals descend to what is probably the normal 



* [Treated as in earlier papers of this series, these lurvte 



a 



c 



^ 



\ 





 25 

 69 

 27 

 40 



\ 





P. 



p 3 



.5 =3 



Both sets of figures point to 50 fathoms being the preferred horizon ; but the total numbers arc unfortunuttlv 

 small.— G. H. F.] 



