272 THE PHYSIOLOGY OF REPRODUCTION 



found impossible to induce erection by stimulating the nervi erigentes 

 in three cats which were castrated when about half, grown and after- 

 wards allowed to reach their full size. It is possible, therefore, 

 that in such animals the muscular apparatus of the penis fails to 

 develop sufficiently to admit of erection occurring, but it would seem 

 unlikely that the nervous mechani'sm is impaired. If erection is 

 due mainly to an inhibition of the vaso-motors of the penis, as is 

 ordinarily supposed, there would seem to be no theoretical reason 

 why it should not -be possible to bring about that process experi- 

 mentally in castrated animals. . It is conceivable, therefore, that the 

 process of erection is after all a more complex phenomenon than is 

 generally believed, but our experiments throw no further light on 

 the mechanism of that process,^ 



' Ott and Scott {Contributions from Laboratory of Medico-Ghirurgical College 

 of Philadelphia, 1912) state that injection of prostatic extract causes erection, 

 the length of the penis and the breadth of the.bulb being considerably greater, 

 than after injection of testicular, ovarian, parathyroid, or pituitary extracts. 



[Note to p. 262. The reproductive organs of bats, and the evidence as to 

 their manner of copulation are described by Wood. Jones (" The Genitalia of the 

 Cheiroptera," Jour, of Anat., vol. li., 1917). ,• The process appears to occur while 

 the animals are suspended, (See also Wood Jones, Jour, of Anat., vol. li., for 

 genitalia of Tupaia.) Meek has given an account of the genital organs in the 

 Cetacea. In the porpoise {PAoccendaommwnis): the penis consists of two portions, 

 proximal and terminal ; during erection the terminal part remains pliable and 

 takes on a corkscrew-like movement, the proximal part becoming hard and 

 rigid (" The Eeproductive Organs of the Cetacea," Jo^or. of Anat., vol. lii., 1918).] 



