38 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 95 



lobes; in some forms (fig. 12 B) it is much shorter than in the 

 Phalangidae. 



During mating of the phalangids, according to Henking (1888), 

 the male and female stand face to face, and the male thrusts the penis 

 into the genital opening of the female, its tip apparently entering the 

 aperture of the ovipositor, since there is no other approach to the 

 seminal receptacles. When the eggs are discharged they must traverse 

 the excessively slender duct of the ovipositor ; Henking records obser- 

 vations on Liobunmn hemisphaericmn in which he followed the transit 

 of the eggs through the duct and saw their exit from its distal end. 

 Since the duct has no muscular sheath, the eggs must be propelled 

 through it, as noted by Rossler (1882), by the action of the bulbus 

 ejaculatorius, which thus has a corresponding function in both the 

 male and the female. The eggs of Liobunmn are deposited in the 

 ground. 



VII. CRUSTACEA 



The crustaceans, by comparison with the progoneate arachnids and 

 diplopods or with the opisthogoneate chilopods and hexapods, might 

 be said to be " mesogoneate ", inasmuch as the genital openings are 

 on the intermediate part of the body. However, if the numerical posi- 

 tion of the segments is considered, the genital segment of some of 

 the many-segmented branchiopods may be as far behind the mouth 

 as that of the chilopods, and considerably to the rear of the genital 

 segments of insects. The segmental position of the gonopores is 

 highly variable in the Entomostraca, but in this group the apertures 

 are always on corresponding segments in the two sexes ; in the Mala- 

 costraca the genital openings are fixed with specific segments, but 

 they are always on different segments in the male and the female. 



To enumerate the postoral trunk segments of the Crustacea in con- 

 formity with the enumeration followed in the Chelicerata, we must 

 begin with the somite of the second antennae, which morphologically 

 corresponds with that of the chelicerae. 



The gonoducts of the Entomostraca usually open separately to the 

 exterior ; in some cases the gonopores are on the limb-bearing thoracic 

 region of the body, but more generally they occur on the abdomen. 

 Intromittent organs are present in some groups, as in Branchiopoda 

 and Ostracoda, the males of which may have a pair of penes, or a 

 single penis through which both vasa deferentia discharge. Examples 

 of the paired type of organ are shown here in two branchiopod 

 species, Branchipus serratus (fig. 14 A, B) and Polyartcmia haseni 

 (C). The two penes of the first species are short, thick papillae 

 (A, Pen) projecting ventrally from the under surface of the second 



