Chap, xiii.] OVIDUCTS OF VERTEBRATES. 511 



greater physiological importance, and give to this out- 

 growth the function of a respiratory organ. 



The fate and functions of the membranes of the 

 mammalian ovum will be considered a little later 

 (page 515). 



In the lower Vertebrates there are no special 

 efferent ducts for the genital products ; as in the 

 Chsetognatha, these fall into the coelom, and make 

 their way into the surrounding water through the two 

 abdominal pores ; in the Cyclostomata these pores 

 represent, no doubt, the primitive mode of exit of the 

 ova and spermatozoa, but in the higher Teleostei, 

 where, again, they (or parts called by the same name) 

 have the same function, it is to be distinctly borne in 

 mind that proper ducts have been there developed, 

 and have subsequently undergone atrophy. 



The arrangement of oviducts which obtains in the 

 frog is that which is most common, indeed almost 

 universal, among Vertebrates ; as in the earthworm, 

 the ova escapes from the ovary into the body cavity, 

 whence they are taken up by the open mor '* of the 

 paired oviducts. These two mouths are sometimes 

 (Elasmobranchs, most Ganoids) fused into a common 

 ostiuin, but the greater part of the ducts are 

 distinctly separated from one another. As has been 

 already pointed out (page 262) these ducts (Mullerian 

 ducts) are derived from the primitive excretory duct. 



In L<epidosiren Hyrtl has described the ab- 

 dominal orifice of each duct as being funnel-shaped, 

 and this form of opening is commonly found in all the 

 pentadactyle Vertebrata. As we ascend the scale we 

 find the oviducts becoming more compact, in so far 

 that the orifice, which in the Amphibia and in the 

 lizard (Fig. 212; ot) lies far forward, and in front of 

 the ovaries, becomes in snakes and mammals set 

 much farther back ; in the latter the oviducts are 

 often spoken of as the Fallopian tubes. 



