36 



STRUCTURE AND CLASSIFICATION OF BIRDS 



ventral bladder of other vertebrates. It is largest in young 

 birds, and often becomes obliterated in older birds. The 

 general relations of the bursa to the cloaca are shown in 

 the two accompanying figures. The organ contains a 

 quantity of lymphatic follicles, and presents us with two 

 types. In most birds it is a diverticulum opening by a 

 narrow neck into the proctodseum ; but in the struthious 

 birds (in the young at any rate) it is not constricted at its 

 orifice into the proctodneum, and the boundaries of the two 

 are therefore indistinct. The structure and arrangement of 



FIG. 22. Two TYPES OF BUKSA. 

 'R, coproclajuni ; C, urodfeum ; D, proctodseum ; B, bursa ; d, ureters. (After FORBES.) 



the follicles and of the bursa generally have led WENCKEMANN 

 to certain classificatory conclusions. 



Reproductive and Renal Organs 



The kidneys are so unimportant from the point of view 

 of the present book that they can be dismissed in a few 

 words. Each kidney is a looulated organ lying in the pelvic 

 region, so closely in contact with the adjacent bones that 

 they are marked by grooves upon the dorsal surface. In 

 some hornbills each kidney is divided into an anterior and 

 a posterior piece, which are perfectly separated. A ureter 

 runs from each kidney to the urodseum. 



The reproductive organs consist of a pair of testes in the 

 male, and of one, rarely two, ovaries in the female. Corre- 

 sponding to the single ovary (the left) is a single oviduct, 

 the right one remaining rudimentary. BALLOWITZ ' has 



1 ' Untersuchungen iiber die Struktur der Spermatozoen,' *c., Arch. Mikr. 

 Anat. xxxii. 402. 



