188 THE VOYAGE OF H.M.S. CHALLENGER. 



the intestine is of greater length than in the carnivorous, so in the case of different specimens 

 of one and the same species of Penguin, the length of the gut may vary in accordance 

 with the more or less nutritive quality of the food at the disposal of different specimens 

 of one and the same species inhabiting different localities. In support of this view, I 

 may refer to the difference in length of the intestine in two specimens of Eudyptes 

 chrysocome. In one of these from Tristan d'Acunha, the gut measured 11 feet 8 inches 

 in length, while in another specimen from Kerguelen the intestine was 23 feet in length. 

 Both of these birds are considered Ijy ornithologists to belong to one and the same species, 

 and yet the length of the intestine of the one is nearly double that of the other. This 

 difference, as well as the smaller differences in the length of the alimentary canal in 

 various specimens of the same species which inhabit approximately the same locality, 

 appears to me to be only explicable on the supposition above enunciated. Be this as 

 it may, difference in length of the alimentary canal cannot j:»er se be considered a 

 reliable factor in the determination of species. 



The Lakge Intestine. 



The large intestine (PI. XIII. fig. 6 and PL XYII. figs. 5, 6, 7, 8) includes the cseca, 

 rectum, cloaca, and anal passage. 



In Eudyptes chrysocome from Tristan d'Acunha, each of the caeca measures ^ an inch 

 in length, and is somewhat dilated at its blind extremity. They are closely applied to 

 one another in front of (below) the termination of the small intestine, the gut passing 

 backwards above them.' Their apertures of communication with the great gut are free 

 and unprovided with any valve. Their mucous membrane presents a reticulated appear- 

 ance, and, unlike that of the small intestine, is altogether devoid of villi. 



The rectum, from the csecal apertures to its opening into the cloaca, measures 1 

 inch in length. Its calibre is of uniform size throughout, and does not exceed that of the 

 small intestine. Its mucous membrane is provided with villi, which, however, are less 

 numerous and more sparsely distributed than in the small gut. 



The cloacal chamber is globular in form, and when distended measures 1^ inches in 

 diameter. When opened, its mucous membrane is seen to be thrown into slightly 

 marked longitudinal rugfe, which are most abundant in the neighbourhood of the rectal 

 aperture. Its surface otherwise is smooth, and presents no trace of villi. On the upper 

 wall of the cloaca there is a well-defined transverse fold of mucous membrane, the 

 posterior border of which is free. This fold indicates the separation of the cloacal 

 chamber into two parts, an anterior larger, and a posterior smaller, which, however, 



' Both Garnot (Annales des Sciences Nat., Zoologie, 1826, p. 53) and Meckel (Anatomie Comjnaree, vol. viii. p. 214) 

 note the close adhesion of the caeca to one another in the Penguins examined by them. Meckel, moreover, states that 

 the caecal cavities communicate directly with one another. Such was not the case in any species which I have 

 examined. In all, the c»cal cavities communicated only with the rectum, each by means of a separate aperture. 



