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



as it passes backwards to its insertion, lies along the outer side of the corresponding 

 ureter, and nearly in contact with the depressor coccygis muscle. In action it would 

 appear that they draw forwards the posterior extremity of the gut, and probably assist 

 in everting the cloaca during copulation and defsecation. 



The sphincter ani consists of a stout bundle of muscular fibres, which surrounds the 

 anus and the posterior extremity of the anal passage. 



Bursa fahricii} — The bursa fabricii varies much in size and structure in difierent 

 specimens of one and the same species. Its size does not appear to be in any way 

 dependent on sex, but rather on functional requirements which influence both sexes 

 alike at various periods. What the nature of these functional requirements really is, I am 

 unable to say. That they are not confined to one sex is abundantly proved by the fact 

 that in some indi^dduals, both male and female, the bursa presents the appearance repro- 

 duced in PI. XVII. fig. 5, where it assumes the form of a relatively small pyriform sac, 

 the blind extremity of which does not extend farther forwards than the middle in length 

 of the globular cloaca. In other specimens, again, the bursa fabricii, when distended, 

 equals, or even exceeds in size the cloaca itself (PI. XVII. fig. 6). 



In those specimens in which the bursa was of small size, whether male or female, I 

 found its lining membrane to be uniformly smooth, thin, and delicate, while in those in 

 which it presented the larger size represented in PI. XVII. fig. 6 the lining membrane of 

 the bursa appeared to have become hypertrophied, and presented a soft, spongy, and 

 succulent character. In the latter the succulent mucous membrane was thrown 

 into well-defined rugse, which for the most part were longitudinal in direction, but 

 communicated freely with one another by means of short, more or less transversely 

 placed folds (PI. XVII. fig. G). The diff'erence in size and structure of the bursa in 

 different specimens of one and the same species is difficult to account for. According to 

 Mr. Forbes,^ the bursa fabricii is of larger size in the young Idrd, and undergoes a 

 process of atrophy as maturity or old age is reached. It is possible that this observation 

 may hold good in the case of the Penguins, as in that of the birds which he examined. 

 At the same time it appears to me to be exceedingly doubtful. The majority of the 

 Penguins at my disposal, as proved by an examination of their skeletons, were certainly 

 adult specimens, and yet the bursa presented the very remarkable variations, both in 

 size and structure, above referred to. In none have I seen it of smaller size than in that 

 delineated on PI. XVII. fig. 5. It seems, therefore, more likely that the variations in size 

 and structure of the bursa fabricii of the Penguin are associated with certain periodic 

 requirements experienced by both sexes, with the exact nature of which, we are still 



' Professor Owen in his paper " On the morbid appearances observed in the dissection of Aptenodytes forsteri," 

 Proc. Zool. Soc, 1865, p. 439, directs attention to the large size of the " urinary bladder," by which I understand he 

 means the bursa fabricii in that bird, and remarks that it constitutes one of the peculiarities in the anatomy of the 

 Penguins as compared with other birds. 



» Proc. Zool. Soc, 1877, p. 304. 



