CLOA CA~COA CHWHIP-BIRD 



91 



that of the rectum proper. In Struthio this chamber is followed 

 by another, which is smaller and less defined, resembling in this 

 respect some Saurians. 



It follows from the arrangement described above, that in Birds 

 the urine is not retained in the small urodiBum, 

 but that, as in Saurians, it passes into the next 

 chamber above. Through this the faeces pass ; 

 if they are very fluid, they collect in the then 

 very capacious space, together with the urine, 

 and transform the chamber into a physiological 

 cloaca. If the faeces are more solid, as for 

 instance in Geese, they are retained in the 

 rectum proper, and simply pass through the 

 cloaca. In the Ostriches deftecation and 

 micturition are mostly separate acts, especially 

 when the largely-developed and persistent bursa 

 Fabricii acts as a physiological bladder. A 

 true urinary bladder, i.e. a ventral dilatation of 

 the urodseum, is absent in Birds. 



Diagram of the 

 Cloaca of a Bird. 



BF. Bursa Fabricii ; 

 CD. Coproda?um; V.D. 



The copulatory organ in the male, and the urocig;um;P.i>. Procto 

 corresponding part in the female, are developed ''^"™ > ^- Rectum ; v. 

 from the ventral wall of the vestibulum or ferens.' 

 " proctodteum." It is present in two different 

 forms. In the Ratitae, except Rhea, it consists of a right and left 

 united half, with a deep longitudinal furrow on the dorsal side, and 

 strongly resembles the same organ in Crocodiles and Tortoises ; it can 

 be protruded and retracted by special muscles which in the Ratitse 

 are partly attached to the pelvic bones. In Rhea, and among the 

 Carinatse in the Anseres only, the copulatory organ consists like- 

 wise of two halves with a longitudinal furrow, but is greatly special- 

 ized by being spirally twisted and being reversible like the finger 

 of a glove ; its muscles are derived solely from the sphincter muscle 

 of the vent. In other Carinatfe, for instance in the Tinamidse, 

 Cracidse, in Platalea, Ciconia, and Phoenicopterus, the penis is much 

 smaller and simpler in structure, with all the appearance of a 

 degraded organ. In the majority of Birds, especially in the highest, 

 it has disappeared, and the primitive way of everting the cloaca is 

 resorted to during copulation (H. Gadow, Phil. Trans. 1887, 

 p. 32). 



COACHWHIP-BIRD, so called in eastern Australia from its 

 loud full note, ending sharply like the crack of a whip, the Psophodes 

 crepitans of ornithologists, while a second form, P. nigiigularis takes 

 its place further westward. Beside this cu.rious utterance it has a 

 low, inward, melodious song. It inhabits the thickest brushwood, 

 seldom exposing itself to view ; but when seen is very animated in 



