of the Fishery Board for Scotland. 



107 



opening of the valve in the genital papilla would immediately be followed 

 by a free issue of spermatophores. The opening of the valve may be 

 due to the pressure of the second penis as it moves in the first, aided 

 possibly by the forward movement of the fifth pereiopod, which will result 

 in increasing the turgidity of the papilla. 



A portion of white plug material has been found on the penis in more 

 than one crab. One case calls for special mention. 



A large male crab, 6 inches across, hard, was examined at the beginning 

 of June. The second penis was inside the first, the genital papilla was 

 inserted into the beginning of the tube. Projecting from the aperture 

 in the tip of the first penis there was a narrow rod-like white body. At 

 the inner side of the base of the first penis there was a small white mass. 

 On examining the rod with the microscope it was found to be a tube 

 crammed with spermatophores ; on its outer surface there were sperms and 

 spermatophores. The tube was formed of parallel fibres. It was found 

 in one penis only. No spermatophores were found in the lower white 

 mass, which had the same fibrous appearance that the plug has. In no 

 case were spermatophores found in the spermatheca packed in a tube. 

 The tube, if it is the normal condition, may act simply as a sheath inside 

 of which the spermatophores travel. It is formed simply by the intro- 

 duction by the base of the penis of some of the fluid of the spermatheca 

 which had flowed out from the vagina. By working the second penis 

 in piston-fashion the tube was gradually pushed out of the first penis. It 

 had apparently been connected to the white mass at the base. 



The Impregnation of Carcinus m^enas. 



The structure of the intromittent organs and of the spermatheca differs 

 considerably from those of Cancer pagurus. It is not, however, proposed 

 to deal with these differences, but to describe the act of fertilisation so 

 far as it was possible to follow it with the naked eye. It is not likely to 

 be strictly homologous to that in Cancer. 



Carcinus mamas is not apparently incommoded to any considerable ex- 

 tent by captivity, and it is possible to observe the act of impregnation. In 

 the following case the male was put into a glass jar, and a female which had 

 cast the previous night was then introduced beside it (September 16th). 

 The male immediately turned the female, with the assistance of the latter, 

 upside down. The female raised (or extended) its abdomen and brought 

 it outside the abdomen of the male. The male then extended its abdo- 

 men, and rested its telson (bent at right angles to the abdomen) on the 

 thorax of the female between the vulvae, immediately thereafter inserting 

 its penes into the two apertures. These operations took place in a few 

 moments. The male then pushed the penes into the vagina? and drew 

 them out slightly, about once every two seconds, but while under obser- 

 vation intermittently. The male carries the female about with it, and 

 the female is attached to the male simply by the hooked penes. The 

 legs of neither crab are used for attachment. The penis appears to be 

 inserted only a short distance. 



On September 18th the two crabs were still in coitu, but on the 20th 

 they were separate. 



The female was now fairly hard. It was killed on the 20th. 



There were no externally projecting plugs. The spermatheca was filled 

 with a large irregular plug which projected a little way into the vagina. 

 In the vagina from the end of the plug just mentioned to the vulva there 

 was another short plug with a rounded upper extremity ; along its 

 length it showed a slight groove. Eound the external end of the 

 spermatheca and along the vagina there is a layer of gelatinous-like tissue, 



