X THE EXCRETORY SYSTEM 211 



The contents of the bladder are expelled suddenly by the 

 contraction of the muscles of the body wall, which naturally 

 subjects the bladder to a considerable pressure. The ex- 

 pulsion of urine often takes place when the frog leaps, and 

 it is very apt to occur as a consequence of the struggles of 

 the animal if the frog is taken in the hands, as every one who 

 has handled frogs has doubtless discovered. The belief that 

 the content of the bladder of the toad is poisonous is 

 entirely without foundation. 



REFERENCES 



Adami, J. G. On the Nature of the Glomerulus Activity in the 

 Kidney. Jour. Phys., Vol. 6, 1885. 



Beissner, H. Der Bau der samenableitenden Wege bei Rana fusca 

 und Rana esculenta. Arch. mik. Anat., Bd. 53, 1898. 



Farrington, 0. C. The Nephrostomes of Rana. Trans. Conn. Ac. 

 Sci., Vol. 8, 1892. 



Frankl, 0. Die Ausfuhrwege der Harnsamenniere des Frosches. 

 Zeit. wiss. Zool., Bd. 63, 1897. See also Arch. mik. Anat., Bd. 51, 1898. 



Nussbaum, M. Ueber die Secretion der Niere. Arch. ges. Phys., 

 Bd. 16, 1878. Fortgesetzte Untersuchungen, etc. I.e., Bd. 17, 1878. 

 Ueber die Entwickelung der samenableitenden Wege bei den Anuren. 

 Zool. Anz., Bd. 3, 1880. Ueber die Endigung der Wimpertrichter in 

 der Niere der Anuren. I.e., Bd. 3, 1880. Ueber den Bau und die Thatig- 

 keit der Driisen. Arch. mik. Anat., Bd. 27, 1886. See also Anat. Anz., 

 Bd. I ; Zool. Anz., Bd, 20 ; and Arch. mik. Anat., Bd. 51. 



