242 



CRUSTACEA. 



of KoLLAK (No. 77), V. NoRDMANN (No. 79), Claus (No. 66), Vejdowsky 

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

 agreement, so that Achthcres, described by Glaus, may be selected as a type. 

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

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

 limbs (iirst and second antennae). Closer examination, however, reveals the fact 

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

 degree of organisation characteristic of the first Cijclops stage. Not only the 

 mouth-parts, but two pairs of thoracic swimming feet (^j^, p^), lie hidden within 

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

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



A z 



Fig. 115.— Metamorphosis of Achthcres percnriini (after Claus, from Balfour's Text-hook). A, 

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

 sexually mature female. E, sexually mature male. ««i, at-, tirst and. second antennae; 

 md, mandible ; mx, maxilla ; pmi, pvi'^, first and second niaxillipedes ; pi, j)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 niaxillipedes ; g, cement gland ; 

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



the adult rostrum. The position of the two niaxillipedes {jmi'^, ■pm") is of 

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

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

 organs, we recognise the future adhering organ in the form of a s))irally-coiled 

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

 frontal process (~). Glaus 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 Nauplius stages, undergoes ccdysis after a few hours, the larva which 

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



