ORGANS OF GENERATION. 125 



essential elements of the vivifying fluid in the class of Birds, have 

 in general an elongated body terminated at one end by a filamentary 

 appendage or tail. Those of the Passeres, which exhibit some slight 

 varieties of form in the different genera, are characterized without 

 exception by a very long body, and a tail spirally contorted after 

 the fashion of a cork-screw ; they are situated freely in the seminal 

 excretory duct, but within the testicle itself are found enclosed in long 

 pyriform cysts. 



A true Intromittent Organ or Penis is wanting to most Birds; 

 some, however, as the Ostrich, have this part very developed, and 

 traversed by a groove for the passage of the semen ; it is of smaller 

 size, tongue-shaped and grooved, as in Crypturus among the Gallinae, 

 or of a membranous texture and cylindrical, lying in a state of rest 

 folded upon itself, or spirally twisted within the cloaca, as in the 

 Drake. According to the recent researches of Joh. Muller, the varie- 

 ties in the structure of the penis in Birds may be referred to three 

 principal types. 1st, The penis is formed, as has hitherto been ob- 

 served, only in the Two-toed Ostrich, of two solid fibrous bodies, pro- 

 vided superiorly with a web of cavernous tissue which is traversed 

 by a cleft or groove ; a third, more elastic and internally cavernous 

 body, is situated upon the opposite side, and forms the extremity of 

 the penis or rudimentary glans. Erection is the result of the dis- 

 tension of the cavernous tissue. 2d, The glans is wanting and 

 the penis has a seminal groove imbedded in cavernous tissue, and 

 also two fibrous bodies. The extremity of the penis with a continu- 

 ation of its groove is involuted so as to form a sack-like part compar- 

 able to a prepuce, which can be partially everted and again re- 

 tracted by an elastic ligament. This structure is met with in the 

 Cassowary and Three-toed Ostrich or Rhea. 3dly, There is found 

 a small tongue-shaped rudiment of a penis, surrounded by a circular 

 pouch, and either with or without a groove. Examples of this type 

 are furnished by the Bustard, several of the Gallinae, e. g. Cryp- 

 turus, Crax, Penelope, and of the Grallae, as the Heron, Stork, and 

 Flamingo. 



Cloaca. 



The term Cloaca is applied to the terminal bladder-like expansion 

 formed by the rectum before terminating in the anus, which occurs 

 in several Mammalia, as the Marsupials and Monotremes, as well as 



