DISUSE AND ITS EFFECTS. 45 



change of function, inasmuch as they are transformed 

 from urinary to reproductive functions in the female, 

 whilst in the male they are functionless. 



The Oviducts. The history of the excretory organs 

 indicates that the kidneys were larger in the an- 

 cestors of vertebrata than in existing forms, and 

 the urinary excretion was conveyed by a series of 

 ducts to the exterior of the body, whereas the kidney 

 possesses now only one duct, the ureter. Of the once 

 extensive renal system, the higher vertebrata possess 

 relics in the form of the Wolffian bodies and their 

 ducts, structures which are relatively very large in the 

 embryo, but towards the mid-period of intra-uterine 

 life dwindle, and are for the most part present in 

 adults as vestiges. Although the glandular portions 

 of the primitive renal system atrophy, and are per- 

 manently replaced by the kidney, the ducts belonging 

 to them undergo a great change, and become utilized 

 for reproductive purposes. 



In some fish the ova are shed into the abdominal 

 cavity from the ovary, and then escape to the exterior 

 by small openings near the anus, known as genital 

 pores. In many fish the ducts which belonged to the 

 anterior section of the primitive kidney become modified 

 into egg-conduits or oviducts. 



When dealing with the Laws of Variation, Darwin 

 states that " a part developed in any species to an 

 extraordinary degree or manner, in comparison with 

 the same part in allied species, tends to be highly 

 variable." This law may be extended beyond the 

 scope, of species, and applied to the 



