MONOTREMATA. 



403 



Fig. 198. 



Mammary gland, Ornitharhynchns, nearly arrived at 

 full size. ( Mcchd.) 



Geoffrey lias argued (Annales dcs Sciences 

 Nut, ix. 1826, p. 457) that the subcutaneous 

 abdominal glands considered by Meckel as 

 mammary, possess none of the characters of a 

 true mammary gland ; he states that he exa- 

 mined them with the greatest attention, com- 

 paring them with the human mammary glands, 

 and especially with those of Marsupial animals, 

 and that they were of a totally different texture, 

 consisting of a vast number of cacums placed 

 side by side, all directed to the same point of 

 the skin, where only two excretory orifices were 

 to be perceived, and these orifices so small 

 that the head of the smallest pin could not be 

 made to enter them. That above all there was 

 no trace of nipples ; that in the specimen 

 examined by him, which had the size and ap- 

 pearance of an adult female, the apparatus in 

 question was not more than a fourth part the 

 size of that observed by Meckel. But a mam- 

 mary gland, Professor Geoffroy observes, when 

 arrived at its full development, occasions an 

 enlargement of all its constituent parts, the 

 nipple acquiring additional bulk even before 

 lactation commences, and that there was no 

 appearance of this kind in the Ornitho- 

 rhynchus. He considers, therefore, these ab- 

 dominal glands as analogous to those which 

 are situated along the flanks of Salamanders, 

 and still more to the odoriferous glandular ap- 

 paratus which is concentrated at the sides of 

 the abdomen in the Shrews. 



In the absence of direct testimony of the 

 nature of the secretion of the abdominal sub- 

 cutaneous glands of the female Ornithorhyn- 

 chus, the next obvious step was to test their 

 disputed nature and office by an examination 

 of their periods of increase and functional 

 activity, as compared with those of the ovaria. 

 If these glands had been analogous to the scent- 

 glands of the flanks in the Shrews, and if their 

 secretion had been destined to attract the male 

 to the sexual intercourse, as suggested by Pro- 

 fessor Geoffroy, their development ought to 

 have proceeded pari passu with that of the ova- 

 ria, and the enlargement of both organs ought 

 to have simultaneously reached its maximum. 

 But in specimens in which the ovisacs were 

 enlarged so as to indicate the ova to be ripe 

 for development, I found* that the abdo- 

 minal glands had made a comparatively slight 

 progress to their full size (Jig. 199). This 

 Fig 199. 





Slannnary gland, Ornithorhynchus, natural size at 



non-breeding season. 

 (Owen, Phil. Trans. 1832. ) 



* Philos. Trans. 1832, p. 525. 

 2 D 2 



