of the Fishery Board for Scotland. 



105 



genital papilla is pressed up against the edge of the sternum the intro- 

 duction is aided. The coxopodito of the fifth pereiopod abuts into the 

 narrow neck of the abdomen at the first and second segments, and the 

 genital papilla lies just beneath the first penis. 



Occasionally a male has been found in which the second penis was 

 inside the first, but usually they are separate. When the united penes are 

 inserted into the vaginae, the abdomen is fixed at both ends. The telson 

 lies on the thorax of the female, and the beginning of the abdomen is 

 fixed at its proximal end by its connection to the thorax. The first penis 

 is then held firmly, but is capable of retraction and re-insertion. The second 

 penis is, however, free to work up and down in the first penis quite 

 independently of it. See figs. 44 and 45. In fig. 44, which is intended 

 to represent the position occupied by the abdomen of the male during 

 coition, A and B are the fixed points. B being the thorax of the female, 

 A the carapace of the male crab. The abdomen of the female is outside 

 and closely applied to the abdomen of the male. The drawing shows the 

 condition in which the second penis is completely entered into the first, 

 and its tip appears projecting outside the tip of the first. In this position 

 it is to be noted that joints 2 and 3 are extended, i.e. the joint between 

 them is depressed. In the drawings they are shown upside down. 

 Now by the flexing of joints 2 and 3 the second penis is withdrawn 

 partly from the first, while the first remains stationary (fig. 45). By 

 each movement the second penis presses on the genital papilla, and 

 therefore probably causes the issue of spermatophores into the tube. 

 The efficacy of the pumping arrangement was demonstrated experi- 

 mentally. A small quantity of a thin carmine paste was introduced 

 into the bottom of the tube, and by alternately pushing in and 

 withdrawing the second penis the carmine was pumped out at the top. 

 By the flexion and extension of the portion of the abdomen, then, the 

 sperms (spermatophores) would be gradually transferred to the spermatheca, 

 into which the first penis penetrates. 



The Condition of the Spermatheca. 



If the soft female crab after it has been impregnated is examined, it 

 will be found that the mouth of the spermatheca and the vagina is filled 

 up by a large plug of white material (pi., fig. 49). This plug may be usually 

 split into two halves, as was shown in a previous paper.* The sperma- 

 theca is globular in shape and is filled with an amber-coloured fluid, and 

 a more or less extensive white patch of sperms, situated in the proxi- 

 mal and external part of the organ. The top of the plug which extends 

 just within the spermatheca is soft and pulpy, being in contact with the 

 fluid, whereas in the vagina the plug is hard and fibrous in appearance. 

 It has been noticed that the top of the plug has been grooved or scored 

 as if a thin body had been repeatedly impressed in it. 



In a hard female crab which has been impregnated the spermatheca is 

 of much smaller size than in the soft crab (fig. 67). It is then 

 flattened, shrunk, disc-shaped, and contains a quantity of sperms (sp.) and 

 some amber-coloured bard material {si.), which is the solidified remains of 

 the fluid which filled the spermatheca at the time of fertilisation. The 

 inner wall of the spermatheca (sp.iv.) and the vagina (v.tv.) are con- 

 tinous, but that of the spermatheca is much the thinner (fig. 38). 



In my previous paper on Cancer pagur 'us I stated that the inner lining 

 of the spermatheca and the contents of the latter were thrown off with 

 the cast integument during the moult, an opinion held also by Cano. 



* " Contributions to the Life History of the Edible Crab (Cancer pagur ns)." Eighteenth 

 Ann. Report of Fishery Board for Scotland, Pt. III., 1900. 



