394 GEOLOGICAL SURVEY OF THE TERRITORIES. 
differ in any important respect from the thoracic limbs, since the abdo- 
men in these families is not differentiated from the anterior part of the 
body. Indeed, if an abdominal leg were exhibited to us separately and — 
placed side by side with a thoracic leg, it would be mere guess-work to 
distinguish them. The only distinction between the two regions, or the 
so-called abdominal and thoracic legs, is the fact that in the Apodide 
the eleventh pair contains the end of the oviduct of the female or vas 
deferens of the male. In the Apodide the gonopods or ovisac-bearing 
legs have been described. 
Kozubowski has discovered and described the male outlet for the 
seminal fluid on the eleventh pair of feet of Apus cancriformis. The 
short vas deferens ends in a minute cup-shaped opening on the gnatho- | 
base or coxal lobe of the eleventh pair of feet. (Gerstaecker’s Arthro- 
poden.) 
The abdominal legs succeeding the eleventh pair lose somewhat of 
their char: acteristic features, until the terminal pairs assumea generalized 
form; the endites, including the gnathobase, being equal in size and 
appearance except the last (sixth), which differs mainly only in being 
larger; the gill is small, while the flabellum is in proportion large and 
orbicular with a few large setulose sets, instead of the fringe of fine, 
short, cilia-like setz edging the exite. 
As to Limnetis, Grube states. that the narrow opening covered by a 
rather long lamella in the last three limb-bearing segments of the body 
may prove to be the male porus genitalis. The eggs are held in place 
by the ovigers of the last three segments in the female. The upper lobe 
of the flabellum of the last pair of feet appears, as seen in fig. 4 (in 
text), to be enlarged and modified to hold the eggs, and I have found 
the freshly extruded eggs heid by the ovigers of the last thrée pairs of 
appendages, so that we may conclude that in Limnetis the last three 
segments of the body form what we may regard as corresponding to 
the abdomen, although the distinction is a somewhat arbitrary one. 
Inreferenceto the male opening in Hstheria nothing is known, as Grube 
states. He thinks he found the cpening of the oviduct of the female 
at the base of the ninth and tenth pairs of feet. Should the hole he dis- 
covered be proved to be the genital pore, then the part posterior to the 
eighth pair of legs should be regarded as abdominal; and thus, in this 
respect, the abdomen in its general relations would compare with the 
abdomen of the Apodide. 
Spangenberg has disccvered the genital opening in Limnadia. “The 
position of the [oviger| on the 11th pair of feet, as well as the general 
agreement in the structure of the Phyllopods, have enabled me to dis- 
cover the hitherto hopelessly-sought-for sexual opening. It lies, cer- 
tainly as in Apus, on the basal joint of the 11th pair of feet; but it is 
very difficult to find if the oviduct is not very full of the shell-forming 
secretion. Except the lengthening of its gill-appendages (oviger), which 
it shares with the two feet in front, the 11th foot undergoes no change 
with the reproductive function.” 
The last joint of the abdomen (urosome), viz, the telson, is only in 
one genus produced into a median spine-like process. This is seen in 
Lepidurus. ‘This spine-like process is seen in the fossil Phyllocarida, 
and in common in the Malacostracan Crustacea. 
The telson itself, particularly the tergal or spinous portion, in Lepi- 
durus, as in Decapods (shrimps, lobsters, ete.), forms the roof or upper 
wall of the rectum, and may thus be functionally compared with the 
- labrum of the head, which, like the spinous portion of the telson, is a 
median unpaued process. The cercopoda, on the other hand, may be 
