102 Part III. — Twenty-second Annual Report 



the vas deferens. The hole in the ccxopodite round which the base of the 

 papilla is attached is situated close to the proximal edge of the bone, and 

 when the limb is drawn forward the base of the papilUa is pressed up 

 against the edge of the sternum of the thorax {cp., figs. 39 and 41). The 

 effect of this is to render the papilla more tense and erect. The outer 

 skin is invaginated into the end of the vas deferens. Within the papilla there 

 is on the vas deferens a valve (v., fig. 47) surrounded by a white mass, 

 probably muscular. The genital papilla has been termed the penis 

 (Duvernoy*). It is not the penis in Cancer pagurus ; it is a physical 

 impossibility for the genital papillae to reach the vulvae of the female. 

 The sperms have to be transferred from the papilla by means of the 

 abdominal appendages. The remaining genital organs are the abdominal 

 appendages. They are attached to the first and second segments and are 

 very dissimilar in form. They are in fact complementary. The first 

 appendage is of tapering shape, and is tubular. The tube is formed 

 by the involution of its sides. The second appendage is a long rod, 

 bent, and jointed about the middle of its length. DifTerent authors have 

 ascribed different functions to these appendages. Thus they have been 

 regarded as " exciting organs," which were introduced into the vaginae of 

 the female, and on being withdrawn their places were taken by the genital 

 papillae. Duvernoy described the first abdominal appendage as a duct 

 for transferring the sperms from the " penis " (genital papilla) to the 

 spermatheca ; the second abdominal appendage he supposed to be a sort of 

 strut, which rested on the thorax of the female and thus formed a sort of 

 prop between the male and female when in coiiu. Neither of these 

 descriptions meets the fact. The first and second abdominal appendages 

 together form one organ, the penis. The second or rod-like appendage is 

 during copulation inclosed within the first penis and moves up and down 

 in it like the plunger of a pump. 



It is first necessary to describe the abdominal appendages in detail. 

 The first appendage, which will be hereafter referred as the first penis 

 (while the second abdominal appendage will be denominated the second 

 penis), is the more complicated. 



The First Penis. 



The first segment of the abdomen bears a large chevron-shaped 

 expansion on its ventral surface (fig. 65). This chevron is really 

 double; a small chevron (i.ch.), which is united with the larger 

 {cell., fig. 46) posteriorly, is hid beneath the latter anteriorly. The double 

 chevron is continued backwards on either side as a broad wing-like plate, 

 at the end of which is attached the first penis (1 j).). The first penis 

 consists of two parts, a short basal joint and a long tubular distal part 

 (fig. 37). The basal joint consists of a peculiarly shaped bone (&., figs. 

 ib. and 59) to which is attached some loose membranous tissue. The 

 membranous tissue is shoAvn in the sketches by dotted areas. The 

 involution of the two sides of the distal portion forms a single tube open- 

 ing by the separation of the two sides at the top. The opening is 

 towards the median line. Fig. 25 shows a transverse section of the first 

 penis near the tip, with the second penis in situ. The outer skin of the 

 penis is hard bony chitin, but lining the tube the inner surface is soft 

 flexible membrane. The latter is shown in the sketches by a thick 

 black line. Fig. 16 shows an intermediate section, and fig. 4 exhibits a 

 transverse section near the base. It shows the sides of the penis drawn 



* Puvernoy, "Fragments sur les organes de g^n^ration de divers animaux." 

 Memoires de I'Academie des Sciences de I'Institut de France, t. xxiii., p. 105, PI. I. -IX., 

 Paris, 1853. 



