394 GEOLOGICAL SURVEY OF THE TEERITORIES. 



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 

 distingTiish them. The only distinction between the two regions, or the 

 so-called abdominal and thoracic legs, is the fact that in the Apodidce 

 the eleventh pair contains the end of the oviduct of the female or vas 

 deferens of the male. In the Apodidce the gonopods or ovisac-bearing 

 legs have been described. 



Kozubowskl 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 jjair of feet. (Gerstaecker's Arthro- 

 pod en.) 



The abdominal legs succeeding the eleventh pair lose somewhat of 

 their characteristic 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 

 largei-; the gill is small, while the flabellum is in proportion large and 

 orbicular with a few large setulose setse, instead of the fringe of fine, 

 short, cilia-like setne 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 poms genitalis. The eggs are held in plax3e 

 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 toehold the eggs, and I have found 

 the freshly extruded eggs held by the ovigers of the last three pairs of 

 ap])endages, 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. 



lu reference to the male opening in Esilieria nothing is known, as Grube 

 states. He thinks he found the opening of the oviduct of the female 

 at the base of the ninth and tenth ijairs of feet. Should the hole he dis- 

 covered be proved to be. the genital pore, then the part i)Osterior 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 Apodidce. 



Spangenberg has discovered the genital opening in Limnadia. "The 

 position of the [ovigerj on the 11th pair of feet, as well as the general 

 agreement in the structure of the Phyilopods, have enabled me to dis- 

 cover the hitherto hopelessly-sought-for sexual opening. It lies, cer- 

 tiiinly 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 Ibot 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 Fhyllocarida, 

 and in common in the Malacostracan Crustacea. 



The telson itself, particularly the tergal or spinous portion, in Lepi- 

 durus, as in Decapods (shrimps, lobsters, etc.), 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 unijaired process. The cercox)oda, on the other hand, may be 



