1886.] Cloaca and the Copulatory Organs of Amniota. 267 



Then the anal sacs or cloacal bladders of the Chelonia are critically 

 discussed with reference to experiments on their being able to take in 

 water. 



Then follows a discussion of the peritoneal canals. 



The cloacal and copulatory organs of the Chelonia lead with com- 

 paratively slight modifications to the Monotremata, from which again 

 a continuity of stages up to the highest Placentalia can be traced. 



The whole cloaca of the Amniota consists originally, either per- 

 manently or in the embryo only, of three successive chambers which 

 may be distinguished as follows : — 



I. The Proctodeum (termed thus by Professor Lankester). It 

 is the outermost anal chamber of epiblastic origin. With 

 its derivatives: (1) Bursa Fabricii in birds; (2) various 

 hedonic glands in most Amniota ; (3) the copulatory 

 organs, the at least partly epiblastic nature of which is 

 indicated by the frequently developed horny armament of 

 the glans, by the various sebaceous glands, and as shown in 

 this paper by its development. 

 II. The Urodaeum, from odpov and haiov. Hypoblastic. This is 

 the middle chamber or primitive cloaca, into which open 

 the urinogenital ducts, and through which pass the fasces. 

 With its differentiations : (1) urinary bladder, ventral ; 

 (2) anal sacs in Tortoises, dorsal, 

 III. The Coprodasum, from Koirpoa and haiov. This is the innermost 

 cloacal chamber. 



The Urodaeum is the oldest portion of the whole cloaca, then 

 follows the Proctodeum, and, lastly, the Coprodaeum has secondarily 

 assumed cloacal functions. 



The various modifications of these three chambers, their function, 

 and the gradual separation of fasces, urine, and genital products have 

 been discussed in the third chapter, and are summarily explained in 

 a table. 



A short note on the presence of Muellerian ducts in the males, and 

 of Wolffian ducts in the females of young Crocodilia. 



Lastly, general conclusions regarding the phylogenetic developmoit 

 and the homologies of the copulatory organs of the Amniota. 



