104 



6. In some orders of mammalia the testicles never leave the 

 abdomen, and in others they descend at certain periods. 



7. There is no general law for the presence or absence of vesi- 

 culae seminales or prostate, the latter is more generally present . 



8. The penis in many instances is furnished with a bone ; in 

 some it is bifid, and in the ornithorhynchus no urine passes 

 through it. 



9. The generative organs and mode of generation are peculiar 

 in the monotremata. 



CHAPTER XIX. 



URINARY ORGANS IN THE INVERTEBRATA. 



The urinary, like the biliary and lachrymal apparatus, consists 

 of four principal parts, each having its peculiar office consigned to 

 it, and all jointly contributing to the same end — namely, the sepa- 

 ration from the blood, and the discharge from the system, of certain 

 decomposed and effete animal and saline matters. The urinary 

 organs, when complete, as they are in the higher orders of animals 

 consist of the kidneys, the ureters, the bladder, and the urethra. 



Although the mollusca secrete urine, and uric acid has been de- 

 tected in the long convoluted caeca of insects, and even through 

 the bodies of cantharides ; yet no perfect urinary system has been 

 discovered in the great invertebrate division of animals. It is more 

 than probable that the function of the kidneys in the majority of 

 instances devolves on the respiratory, the cutaneous, and the biliary 

 systems, together with certain glands, many of which serve not only 

 for the elimination of noxious materials from the system, but as or- 

 gans of defence on the approach of danger; in this latter light may 

 be regarded the acrid secretions of bees, beetles, wasps, and spiders ; 

 as also the ink of the cuttle-fish which has the effect of blackening 

 a considerable extent of the surrounding water, and thus baffling 

 the attacks of its enemies : and among the vertebrata, a striking 

 example is presented by the yagouare of Azara, one of the mephitic 

 weasels of Chili, whose urine is rendered so intensely offensive by 

 the secretion of some adjoining glands, that dogs or other animals 

 which have been sprinkled with it during their pursuit of this crea- 

 ture, are said to have torn portions of their own skins off from dis- 

 gust, notwithstanding careful and repeated ablutions. 



