242 



CRUSTACEA. 



of Kollak (No. 77), v. Nordmann (No. 79), Claus (No. 66), VEJDOWSK 

 (No. 81), and others. Its course in the various forms seems to show gre 

 agreement, so that AchtJieres, described by Claus, may be selected as a typ 

 The young animal which hatches from the egg (Fig. 115 A) exactly resembles 

 Nauplius, swimming about with difficulty by means of its two anterior pairs 

 limbs (first and second antennae). Closer examination, however, reveals the fa 

 that the body which is hidden within the Nauplius cuticle already shows th 

 degree of organisation characteristic of the first Cijdops stage. Not only tl 

 mouth-parts, but two pairs of thoracic swimming feet (p 1 , p' 2 ), lie hidden with 

 the Nauplius integument. The mandibles (md) and first maxillae {mx) lie 

 small stumps at the sides of the upper lip, which enters into the formation 



Fio. 115.— Metamorphosis of Achtheres percarum (after Claus, from Balfours Text-book). A, 

 so-called Nauplius stage. B, first Cyclops stage. C, older stage of the male larva. J>, 

 sexually mature female. E, sexually mature male. at\ afi, first and second antennae ; 

 md, mandible ; mx, maxilla ; pm 1 , pvifi, first and second maxillipedes ; p 1 , p 2 , first and second 

 swimming limbs ; z, frontal organ ; i, intestinal canal ; o, Nauplius eye ; b, glandular body ; 

 t, organ of touch ; ov, ovary ; /, spine derived from the fused maxillipedes ; g, cement gland ; 

 rs, receptaculum seminis ; n, nervous system ; tc, testis ; v, vas deferens. 



the adult rostrum. The position of the two maxillipedes (pm l , pm 2 ) is of 

 Interest, in so far as it proves distinctly that they develop as the exopodite and 

 cndopodite of one and the same limb (second maxilla). Besides the above 

 organs, we recognise the future adhering organ in the form of a spirally-coiled 

 filament ending in a spherical swelling which grows out from a highly-refractive 

 frontal process (2). Claus considers that this apparently homogeneous filament 

 is a tube filled with a fluid secretion, and is the duct of a glandular mass which 

 secretes a cementing medium. This first stage which seems to cover the whole 

 series of Naicplius stages, undergoes ecdysis after a few hours, the larva which 

 follows possessing the organisation of the first Cyclops stage (Fig. 115 B). It 



