224 CONTRIBUTIONS TO MA.RTNE BIONOMICS. 



It caunot be said, however, that the real position and affinities of the 

 Corystidoe are yet established. The reason for this uncertainty is 

 probably due to the fact that, as will appear further on, the structure 

 of these animals is remarkably modified in relation to sand-burrowing 

 habits. Some of these adaptive modifications of structure, which re- 

 appear in certain other groups of Crustacea, have undoubtedly impressed 

 the minds of certain writers with ideas of homology and genetic re- 

 lationship between the Corystida3 and groups having no real affinity 

 with that family. The case affords a new illustration of the inadequacy 

 of the purely morphographic method, when unchecked by considerations 

 of functional adaptation, for the solution of problems of relationship 

 and genetic classification. 



II. Structural Peculiarities. 



The structure of Corystes cassivclaunus is noteworthy on account 

 of the following features. The second antennte are greatly elongated — 

 as long as, or longer than, the body — and are fringed along their entire 

 length by two rows of hairs, one of which runs along the ventral, while 

 the other runs along the dorsal border of the antenna. The hairs of 

 each row curve inwards towards those of the corresponding row on the 

 second antenna of the opposite side. The second antennse shew a 

 marked tendency to approximate to one another longitudinally; the 

 opposing rows of hairs then interlock, with the resulting formation of a 

 median tube, the lateral walls of which are formed by the jointed 

 flagella of the antennoe, while the dorsal and ventral walls are fenes- 

 trated along their whole extent by the interspaces between the inter- 

 locking hairs. The organ formed by the apposition of the second 

 antennae I shall term the " antennal tube." 



The long axes of the three stout basal joints of the second antenna 

 are disposed at right angles to one another, and bring about a character- 

 istic double bend in the basal part of the antenna. The double row of 

 hairs found on the flagellum of the antenna is continued backwards 

 along these three basal joints. The hairs on the most distal of the 

 three joints interlock with those of the corresponding joint of the 

 opposite antenna ; the hairs on the anterior face of the deflected middle 

 joints bend inwards towards the median line along the sides of the 

 rostrum, and together with a median triangular tuft of hairs springing 

 from the rostrum itself, form the hairy roof of the proximal part of the 

 antennal tube. 



The antennal tube opens posteriorly into a rectangular chamber in 

 front of the mouth. This " prostomial chamber," as it may be termed, 

 is roofed by the rostrum in front, the antennal and epistomial sternites 



