282 FROGS, TOADS, AND NEWTS [CH. VIII 



prominent at the breeding season, whereas that of the 

 female is cylindrical. From this ridge arises a muscle 

 (flexor carpi radialis) which is also in vigorous action while 

 the male embraces the body of his mate. While pairing 

 is in progress and prior to it the male frogs often keep up 

 a chorus of croaking. At a distance of twenty or thirty 

 yards the noise made by a number all croaking together 

 is not displeasing, and might be mistaken for the cooing of 

 a pigeon. The females also croak loudly and appear to 

 inflate the floor of the mouth as they do so. It is 

 noteworthy that the animals can croak when several 

 inches below the surface of the water, and that the noise 

 can even then be heard at a distance of several yards. 

 The noise is produced by the vibration of two vertical flat 

 bands of connective tissue, the vocal cords, which project 

 into the cavity of the larynx, or upper portion of the very 

 short windpipe ; the position and tension of these cords 

 can be varied and regulated by certain muscles which 

 move the cartilages to which the cords are attached. 



When the ovaries are ripe they shed their contents 

 into the body cavity. The exact method by which the 

 ova find their way into the oviducts is not fully under- 

 stood. According to Nussbaum 1 in Rana fusca certain 

 parts of the peritoneal lining of the body cavity are 

 ciliated. Presumably by the action of the cilia and pos- 

 sibly also by contraction of the abdominal muscles the ova 

 are driven forward into the region of the oviducal apertures 

 and eventually forced into them. The ciliated internal 

 lining of the oviducts forces the ova backwards along the 

 convoluted tubes towards the cloaca. In course of transit 



1 Arch. f. mikrosk. Anat. XLVI, 



