276 



DIDELPHUS. 



sockets ; and from this peculiar structure of the eye, 

 it is probable that the animal sees only at short dis- 

 tances, but that its vision there is quite microscopic. 



Virginian oppossum. 



From the structure of the nose it is presumed that the 

 sense of smell is very acute ; but it cannot be very 

 delicate in our way of estimating ; for in that case 

 the animal would be perfectly intolerable to itself, the 

 odour which it emits when disturbed or threatened 

 being described as one of the most offensive in nature. 

 But there is no subject upon which we are more in 

 the dark, and more likely to remain so, than that of the 

 senses of animals. We know the operations of our 

 own senses very imperfectly ; and in the case of 

 smelling in particular, we are unable to say what is 

 the specific difference of affection in our organs, 

 which makes us turn with feelings of pleasure to the 

 odour of roses or of new hay, and shun with pain and 

 aversion that of such an animal as the opossum. 

 Now, if we know little of these matters in our own 

 case, where the pleasure is mental, and, whether we 

 understand its foundation or not, a result of reason 

 and experience, and given us as one of the means by 

 which we are to understand the properties of things, 

 and apply them to our uses in the most pleasing, and 

 at the same time, in the most economical manner for 

 the good of the whole ; if we are thus ignorant in 

 our own case, where we have something of more im- 

 portance than the mere animal sensation to guide us, 

 what can we know in the cases of the other animals ? 

 and not knowing, how can we reason ? 



Still, this is a subject upon which it is exceedingly 

 difficult for any body to refrain from speculating, and 

 it is nearly, if not altogether, as impossible for any 

 body to be right in such speculations. We are, 

 however, thus far certain, that no animal can feel what 

 we call mental pleasure from sensation, apart from the 

 office which that sensation may supply in the mere 

 economy of the animal. Thus, for instance, there is 

 no material eye, except that of man, which can see 

 beauty in form or in colour, neither is there any nos- 

 tril, save his, which can scent fragrance, and derive 

 from it those emotions of delight, which we never fail 

 to experience when the healthful breezes come to us 



sporting over beds of flowers. But, if we cannot sup* 

 pose animals have the pleasures of sense, which are 

 mental or supplemental to the mere excitement of the 

 bodily organs, we cannot suppose that they should 

 have the opposite feeling of deformity to the eye, and 

 ungrateful odour to the nose. Upon this principle 

 we can readily perceive that, offensive as the smell of 

 the opossum is to our feelings, it may itself be alto- 

 gether insensible to that odour which instinct teaches 

 it to give out, probably as its chief means of defence. 



In many parts of South America the opossum is 

 so abundant, that it prowls about in the villages, and 

 even in the towns. D'Azzara mentions that they are 

 frequently found lying dead iu the villages near the 

 shores of La Plata, and even in the streets of Monte 

 Video. He was the first to get a correct account of 

 the marsupial apparatus of the female, which we shall 

 give in nearly his own words. " The female has the 

 whole length of the belly cleft or slit, and appearing 

 like a person's waistcoat buttoned only at the top 

 and bottom. This cavity the animal has the power 

 of firmly closing. Within it are thirteen teats, ex- 

 tremely small, one in the centre, and the rest ranged 

 round it." 



Before the female comes to maturity, this marsupial 

 apparatus is but little developed, there being only a 

 slight fold of skin on each side the abdomen. Alter 

 the young are weaned, the marsupium also collapses, 

 and it is gradually reproduced as the time approaches 

 when it is to receive a new litter. There seems 

 indeed to be, so to speak, an alternation of the t\vo 

 systems of gestation in these curious females. The 

 uterus is the place where impregnation is effected, 

 and where the germ is developed, at ieast in its early 

 stage ; but as this takes place when they are in a 

 much more rudimental state than any young animals 

 which pass at once from the uterus to an external 

 mammary system, there is a degree of excitement 

 required in the marsupial apparatus which is not 

 needed in the case of those animals which produce 

 their young comparatively mature, and capable of 

 taking the teat at intervals as nature requires. The 

 perfect marsupial animals, or those which have the 

 internal and external periods of gestation pretty 

 nearly of the same length, remain on the teat, like 

 any moveable excrescence, until they are completely 

 developed ; and it has been ascertained, that in some 

 of the species at least, there is a sort of umbilical cord 

 which connects the young with a sort of placental 

 substance in the body of the teat, until it acquires its 

 form and some of its functions as an animal, at which 

 time it breaks this second connection with the mother, 

 or is born a second time, now an independent animal, 

 capable of drawing milk from the teat, and in due 

 time of finding its food. But this second gestation in 

 the marsupium is clearly as essential to the perfect 

 development of the animal as the first gestation in 

 the internal uterus ; and we can no more imagine an 

 opossum to come to maturity, if it enjoys only the 

 first, and has not its full time in the second, than we 

 can imagine the untimely birth of any other animal to 

 become mature. 



This is a most extraordinary piece of nature's 

 economy, and a part, the design of which we are 

 unable, in the present state of our knowledge, to 

 comprehend, and yet it is one which very powerfully 

 and pressingly tempts us onward to inquire. 



Now, we perceive that this double gestation, by 

 means of the internal uterus and the abdominal pouch, 

 stands as it were midway between the single internal 



