Chap, xiii.] OVIDUCTS. 513 



In the Teleostei, and the teleostean-like Ganoids, 

 such as Lepidosteus, the oviducts have no patent 

 abdominal mouths, but the walls of the tubes are, 

 continuous with those of the gland, or the ducts 

 become more or less aborted ; here it would appear 

 that the oviduct is not the altered Mullerian duct, but 

 sufficient information on this head remains to be 

 acquired. When, as in eels and salmons, the ducts 

 become completely aborted, the ova fall into the body 

 cavity and escape to the exterior by the so-called 

 abdominal pores. 



The different regions of the oviducal canal take on 

 very various functions in various vertebrates; one 

 important factor in determining the character of the 

 ducts is the size of the ova which pass through it, and 

 another is, of course, to be found in the different 

 conditions of size and age in which eggs are laid or 

 young brought forth. In the frog the whole of the 

 canal, with the exception of the penultimate portion, 

 is of the same calibre throughout ; in the terminal 

 enlargement the ova become grouped into masses, 

 which are held together by the gelatinous substance 

 secreted by the oviducal glands ; the ova are fertilised 

 outside the body of the female. In some Elasmo- 

 branchs, and in the Sauropsida, the ova as they pass 

 down the ducts become not only invested by a layer 

 of albumen, but surrounded by a shell ; this may be 

 horny, as in Elasmobranchs, Lacertilia, and Ophidia ; 

 or firmer and calcareous, as in other Reptiles and in 

 Birds. 



In the Ophidia the right ovary is always larger, 

 and often much larger, than the left, and the left 

 oviduct shorter than the right ; in Birds, on the other 

 hand, the right ovary and duct become aborted during 

 development, though indications of their presence are, 

 of course, retained by some forms. 



Where the ova are not only fertilised within the 

 HH 16 



