Stiiilics on rnariiii' Oslrncods 440 



mo as a stuall vcnuriioiiii process situated anteriorly of the e-bristle. Pilosity: The first and 

 second joints are often furnished with more or less abundant groups of fine, short, stiff hairs, 

 often arranged in transverse rows on the second joint. 



Male: — This is not quite so powerfully built as that of the female and is somewhat 

 longer and more slender in comparison. Its joints are not so much flattened at the sides. It 

 lias six or seven joints; the third and fourth joints are always free. The fifth joint is well defined 

 from the fourth; on its proximal edge there are the distal fastenings for no less than three rather 

 powerful muscles. The boundary between this joint and the sixth joint is, <jn the other hand, 

 sometimes not so well developed; sometimes, perhaps, these joints are quite united; the sixth 

 joint is not moved by any specific muscles. The relative proportion of the joints is subject 

 to some variation within the genus. The following figures may be given as examples (the 

 measurements are from A. norvegica, with a shell 2,42 mm. long): 



I ??. n "• III '^- IV ''• A^ -• VI ^^- VII ^ 



For the sake of comparison the corresponding figures for the female are also given here. 

 (The same species as above, with a shell 2,2 mm. long. The scale is the same as above.) 



I %; II ^; III 1; IV ,\; V '}; VI *; VII I. ' 



The proportion between the joints in this antenna of the male and the female consequently 

 differs fairly considerably (cf. also A. curta, p. 501 of this treatise). The fifth joint is rather 

 considerably shortened, its posterior edge is so short that the sensory bristle often seems to be 

 attached close to the two posterior distal bristles of the fourth joint. The seventh joint is very 

 considerably larger than in the female, its posterior edge especially is very considerably lengthened. 

 The boundary between the sixth and the seventh joints is of so irregular a type that mistakes 

 can easily be made. Observation is often rendered difficult, in addition, by the fact that some- 

 times it is not very distinctly developed and that accessory chitinous creases arise. I need 

 only refer here to fig. 11 of ^. Grim.aldi and fig. 7 of A. curta; in the former the contour of the 

 boundary of one side is drawn with an unbroken line, and that of the other side with a dotted 

 litii'. I have been and am almost still in doubt as to whether that part of the end joint on which 

 the (d-), e-, f- and g-bristles are fixed, is really to be considered as a special joint or not. The 

 idea that this part is a special joint is supported especially by the fact that it can move freely 

 by means of two powerful muscles. The fact that I do not accept this interpretation but consider 

 this part as a jjortion of the seventh joint is due entirely to its exceedingly small size; 

 the muscles seem, as a matter of fact, to be fixed directly to the basal part of the bristles.* 

 The number and position of the bristles is the same as in the female; with regard to their 

 development, however, there is a not inconsiderable difference between the two sexes. The 

 lateral bristle on the second joint is somewhat longer than in the female. The anterior bristle 

 on this joint is somewhat weaker. The bristles on the anterior edge of the third joint are 

 also somewhat weaker than in tlie female and are somewhat shortened; sonic of them are 

 I'ven very much shortened. The sensory bristle of tlic fifth joint: In what seems to l)e tlie 



* This pari, is, however, as we know, ilevelo|)e(l as a <lis1iiicl joint in most of llir n|iii'si'nlalives of Ihe sub-rainily 

 f'/lir/flininar. 



Zoolog. bidr.iK, Uppsala, Suppl.-Bil. I. 57 



