MR. OWEN ON THE GENERATION OF THE MARSUPIAL ANIMALS, 349 



act of injection ; and if at any time this should not be the case, a fatal accident 

 mig-ht happen from the milk being forcibly injected into the larynx, unless that aper- 

 ture were guarded by some special contrivance. Professor Geoffroy first described 

 the modification by which this purpose is effected ; and Mr. Hunter appears to have 

 foreseen the necessity for such a structure, for he has dissected two small mammary 

 foetuses of the Kangaroo for the especial purpose of showing the relation of the 

 larynx to the posterior nares=*. The epiglottis and arytenoid cartilages are elongated 

 and approximated, and the rima glottidis is thus situated at the apex of a cone-shaped 

 larynx, which projects, as in the Cetacea, into the posterior nares, where it is closely 

 embraced by the muscles of the soft palate. The air-passage is thus completely sepa- 

 rated from the fauces, and the injected milk passes in a divided stream on either side 

 the larynx to the oesophagus. 



Thus aided and protected by modifications of structure, both in the system of the 

 mother and in its own, designed with especial reference to each other's peculiar con- 

 dition, and affording therefore the most irrefragable evidence of creative foresight, the 

 feeble offspring continues to increase from sustenance exclusively derived from the 

 mother for a period of about eight months. The young Kangaroo may then be seen 

 frequently to protrude its head from the mouth of the pouch, and to crop the grass at 

 the same time that the mother is browsing. Having thus acquired additional strength, 

 it quits the pouch, and hops at first with a feeble and vacillating gait, but continues 

 to return to the pouch for occasional shelter and supplies of food till it has attained 

 the weight of ten pounds. After this it will occasionally insert its head for the pur- 

 pose of sucking, notwithstanding another foetus may have been deposited in the 

 pouch, for the latter, as we have seen, attaches itself to a different nipple from the one 

 which had been previously in use. 



^ 3. Ow the Structure and Analogies of the Female Generative Organs in the Marsupiata. 



In the oviparous vertebrate animals the variations of structure which the female 

 generative organs present in the different classes are fewer and of less degree than 

 those observable in the different orders and genera of the Mammalia. 



The most prevailing characteristic of the oviparous type of the female generative 

 organs is the absence of union in the mesial plane of the lateral efferent portions, 

 which consequently continue separate to their terminations in the excretory outlet. 



In Birds the genital apparatus is characterized by the superior, and in the female, 

 as far as function is concerned, exclusive development of the left moiety ; and the 

 uniformity in the condition of the excluded ovum in this class corresponds with the 

 sameness which prevails in the structure of the organs concerned in its production. 



In Reptiles the ovaries and efferent parts of the genital system are equally developed, 



* See Nos. 3731, 3734, 3735 in the Physiological Series of the Hunterian Museum, in which there are evi- 

 dences that Mr. Hunter had anticipated most of the anatomical discoveries which have subsequently been 

 made upon the embryo of the Kangaroo. 



MDCCCXXXIV. 2 Z 



