42 SMITflSONIAX MISCELLANEOUS COLLECTIONS VOL. 95 



are composed of two pairs of long processes arising from the inner 

 ends of the basal segments* of the first and second pleopods, which 

 are, therefore, probably the endopodites of these appendages (A, B, 

 Endpd). The genital processes, or gonapophyses, of the first pair (A) 

 are expanded distally and hollowed on their inner surfaces ; those 

 of the second pair (B) are cylindrical, and their distal ends fit snugly 

 into the concavities of the first pair (C). By means of these organs 

 the male during mating inserts a pair of large, horseshoe-shaped 

 spermatophores (F) into a two-branched receptacular pouch open- 

 ing on the venter of the last thoracic segment of the female. The 

 spermatophores are probably taken from the gonopores of the male 

 into the cavities of the first gonapophyses, and forced from the latter 

 by the second gonapophyses. Within the receptacular pouches of the 

 female the spermatozoa are discharged from the spermatophores, and 

 the latter are then rejected. Since there is evidence that fertilization 

 of the eggs takes place in the oviducts, it is supposed that the sperma- 

 tozoa are transferred into the openings of the latter on the sixth 

 thoracic segment by means of setigerous lobes, present only in the 

 female, on the inner surfaces of the coxopodites of the last three pairs 

 of thoracic legs. The fertilized eggs are said by Smith (1909) to be 

 deposited singly " under stones and among the roots of water plants " 

 (his figure shows them on the branches of a liverwort). 



The Isopoda generally have two separate genital exit ducts, which 

 in the male open either by simple apertures (fig. 16 A, Gprs) or 

 through a pair of small penes on the sternum of the last thoracic 

 segment. In the Oniscoidea, however, which include the ordinary 

 terrestrial isopods, there is present usually a single median penis 

 (C, D, Pen), and the gonoducts unite at its base in a common exit 

 tube. The median penis may be displaced posteriorly so that it arises 

 from the membrane behind the last thoracic sternum, with its base 

 between the appendages of the first abdominal segment (D, Pen). 

 The intromittent organs of Isopoda, when present, are formed as in 

 Anaspidacea of the inner arms, or endopodites, of the first and 

 second pairs of abdominal appendages (D, E, Endpd). By means of 

 these structures masses of spermatozoa that issue from the gono- 

 pores are inserted into the genital openings of the female. The termi- 

 nal parts of the oviducts in some species of isopods are enlarged to 

 serve as sperm receptacula, and the eggs are fertilized in the ducts. 

 After mating, the female moults and in most species acquires a brood 

 pouch (marsupium) on the under surface of the body, into which the 

 fertilized eggs are discharged, and within which they are carried 

 until the young hatch. The brood pouch is formed typically by broad 



