






28 G Canadian Arctic Expedition, 1918-16 
somewhat square in shape, and convex in front, in the middle of whic 
large nauplius-eye is seen, and with the adjesive organ occupying almost 
centre of the dorsal surface of the head. The composite paired eyes are lai 
with movable, more slender penduncles and of the usual, iridescent, blackish 
colour. Their length is about that of the first pair of antennae situated next to 
them. The second antennae are developed as large sickle-shaped claspers, 
reminding one strongly of the mandibles of certain insect-larvae (Dytiscidae). — 
Their bases are confluent, uniting into the labrum (see below) and more slender © 
than at the level of the composite eyes, where the basal joint is enormously 
swollen (to give room for the powerful muscles) and ends inwardly in a broad 
and flat part, somewhat triangular in shape and ending in a blunt point, well 
shown in the dorsal view. The terminal joint of the claspers resembles a broad 
and flat fish hook, running out into a blunt and slightly curved terminus, and 
with a widening occupied by two hooks a little more than half way down. Each 
clasper is roughly spinose on the whole of the terminal joint, except for the 
proximal half of the central thickest part. At the base of the terminal joint of 
-each clasper is a small hooked spine, on the inner side. The head is without 
frontal process unless a small, heart-shaped appendix, made up of two halves, 
situated between the bases of the two claspers, ventrally, can be considered as 
such ! (fig. 5c). The labrum is broadly spatulate, rounded at its free posterior 
end. Behind it are seen the mandibles and two pairs of maxillae. The two — 
first abdominal segments of both sexes are fused together and much swollen, 
owing to the development of the genitalia. The ventrally protruding part of 
the latter has in the male somewhat the shape of the ‘‘sac” of the Cirriped, 
Sacculina, parasitic upon the tail of crabs. With the fairy-shrimp this ‘‘sac’’ is 
somewhat slender at its base, and occupied by the two coiled penes, their swollen 
bases showing a granulated spiny chitinous and yellow surface (fig. 5d). Thefree — 
ends of the two penes each forma coil somewhat resembling a snail-shell with a few 
loose turns; the spinein which each one ends (see A. bungez) is apparently only pro- — 
truded occasionally, in the actual moment of copulation. The length of the 
abdomen is a little less than that of the body (excluding the head), and has no 
dorsal processes above the genitalia. 
The females (see text fig. 6) are a little larger (8-11 mm.) than the males, 
mainly caused by an elongation of the abdomen. The head (fig. 6a, c) is more 
rounded oblong than in the male, and of course smaller, owing to the little 
deveopment of the second’ pair of antennae. The first pair of antennae seems 
comparatively shorter than in the male, while the second pair is only a little. 
longer than the composite eyes, and of the shape usual with female fairy-shrimps. 
The nauplius-eye, adhesive organ and mouth parts? are of course as with the 
male, as also the body with its foliaceous legs. The first and the last pairs of - 
the latter are shown in fig. 5b and d. They are similar to those of A. bunger _ 
(Daday de Dées, 1910, fig. 17). 
In the female A. stefanssoni the last body segment and the two succeeding — 
abdominal segments are each produced laterally (fig. 6b) into a flap-process (import- — 
ant for copulation-purpose), very similar to the two similar ones found on the same 
part of the b ody in the female Eubranchipus gelidus (Hay). They are, however, 
not lanceolate-triangular as in H. gelidus, but more spoon-shaped. The ovisac 
(fig. 6d) is very large and oval, its transversal diameter being longer than the 
longitudinal. On its ventral side are seen two broad folds in the wall of the 
ovisac probably supporting the latter in its movements. These females, secured | 
on October 6, 1915, had a great number of ripe, red-brown eggs filling the whole 
middle part of the ovisac, the unripe part of the ovarium showing up as two 
smaller masses above the ripe egggs. The abdomen is about the same length . 
as the body, owing to the great development of the ovisac. 
1 It is probably a remnant of the “‘kidney-labrum,” so largely developed in the nauplius and metan- 
auplius stages of fairy-shrimps (see p. 17). : 
2 There seems to be no “‘appendix’’ to the labrum (‘‘kidney remnant”) as with the male; that the 
jatter has it is the only case among fairy-shrimps I know of. 

