1896.] OF THE GBNtrS SEUSBSTES. 943 



legs are at least shorter, more slender, and with fewer hairs than in 

 the adults. But the hest distinction between the larvae and the 

 adults is, as hinted above, the shape and especially the colour of 

 the eyes : in the larvs3 the eye-stalks are almost always long, the 

 eyes are rather large, or even very large, and have an oblique and 

 more or less fungiform shape ; while in the adults the eye-stalks are 

 rather short, and the eyes smaller, more regularly globular, and 

 sometimes but slightly thicker than the distal end of the stalk ; in 

 all larva; the eyes arc yellowish (or wliitisli), and hlaclc jyigmenij when 

 present, is only found in the interior and very remote from the cornea, 

 ivhile in the adidts the eyes are totally black, ]iut it must bo 

 emphasized that even when the black eyes are acquired and all other 

 larval characters have been lost, the animals are still immature, as 

 the petasma is developed somewhat later, and the petasma itself 

 does not become completely developed at once to its final shape. 



Por the rest, more or less conspicuous alterations in all parts of 

 the body and the limbs take place during the development from 

 the youngest Mastir/ojnis-stage to the adult Serc/estes, but it is 

 impossible to give a full elucidation without numerous ligures. 

 Besides, the species show considerable differences in development : 

 thus, for instance, the dorsal abdominal spines are in some species 

 lost when the Mastiyopus is not half-grown, while in other species 

 they are preserved till the Mastigopus is almost full-grown and the 

 colour of the eyes alters, &c. Therefore I do not attempt to 

 give a general picture of the metamorphosis, but I will refer the 

 reader to the following more special, but short treatment of the 

 species. 



Next we arrive at three fresh considerations : (1 ) the separation 

 of the adult species from each other; (2) the discrimination of the 

 larva;, so that the different stages of the same Mastigopus may be 

 referred to each other and separated from other larvfe ; and 

 (3) the reference of any given Mastigopus to its species of Sergestes. 

 In the literature of the subject numerous characters have been 

 used, but some of them are only applicable to the adults, others to 

 the larval forms, and several good characters proposed by Kro er 

 and S. I. Smith have been overlooked, or at least not used with 

 sufficient accuracy, by most authors. The whole question of the 

 characters must be re-examined. 



For the characterization of the adult species must be used 

 differences in the following structures : — the shape of the rostrum, 

 absence or presence of supra-ocular spine, hepatic spine, and gastro- 

 hepatic groove on the carapace, shape and size of the eyes, the 

 relative length of the 3 joints of the antenn. ped.', their size, and the 

 shape of the basal one, the shape of the apical part of the squama, 

 the length and structure of mxp.' (whether the 4 proximal joints 

 are similar to those jn trl.' or are obviously incrassated, the arming 



' In order to abridge the descriptions, I in the following pages make use of 

 some abbreviations: — antenn. ped. = peduncle of the antennulte, mxp.'=tho 

 third pair of maxillipeds, trl.'-trl.*=the first to the fifth pair of trunk-legs, 

 ext. br. of urp.=external branch of the uropods. 



Piioo. ZooL. Soo.~- 1896, No. LXI. 61 



