GENERATION. 



437 



there receives its food by the mouth and is 

 nourished by digestion at an early period of its 

 ailvatie. nient ; and, although its external form 

 and organization very much resemble that of 

 the lii-tiii of other mammiferous animals at a 

 similar stage of their advancement when they are 

 still confined to the uterus of the mother, their 

 internal organization undergoes at the time of 

 their exclusion the same remarkable changes 

 which occur at birth, and which are connected 

 with aerial respiration and the independence of 

 the vital functions.* 



Monotrcmutuus generation. The generation 

 of the Ornithorynchus and other monotrema- 

 tous animals deserves also to be noticed here 

 as differing in some respects from that of other 

 Mammalia; but, unfortunately, this subject, 

 which has been involved in obscurity ever since 

 the first discovery of these remarkable animals, 

 notwithstanding that several important (acts 

 have been recently ascertained, cannot be con- 

 sidered as completely understood. The Orni- 

 thorynchus and Echidna were long regarded as 

 holding an intermediate place in respect to 

 their organization between Mammalia and 

 Birds. The existence of mammary glands was 

 denied by the first dissectors of these animals ; 

 and from this circumstance principally, toge- 

 ther with the analogy in general structure al- 

 ready alluded to, the Ornithorynchus was be- 

 lieved by many to be oviparous. The recent 

 investigations of Owen have proved the ex- 

 istence of mammary glands as well as the 

 suckling of the young, while they at the same 

 time shew that the generative organs and the 

 ova within the ovaries partake in a great degree 

 of the oviparous structured In this approach 

 to the oviparous type, however, it has been 

 satisfactorily shewn that the Ornithorynchus 

 resembles the class of Reptiles rather than that 

 of liirds. The ova of this animal have not, how- 

 ever, been found in any of its haunts; and, 

 Although no one has yet had an opportunity 

 of dissecting the gravid uterus, naturalists are 

 now inclined to hold the opinion that it bears 

 its young alive. Should this be fully proved 

 to be the case, the Ornithorynchus may with 

 justice be considered as an example among 

 mammiferous animals of the ovo-viviparous 

 form of generation, most analogous to that 

 occurring in the Slow-worm or Adder; the 

 ovum being, at the time of its descent into the 

 oviduct, of proportionally large size, and there 

 beino no proper placenta or intimate organic 

 union between the mother and fiztus. 



Comparison of animal and vegetable repro- 



* For the details respecting the structure and 

 functions of (he generative organs of the Marsu- 

 piala, the mode of passage of the embryo from the 

 uterus to the pouch, see the article upon the Com- 

 parative Anatomy of these animals, MARSIIPIATA. 

 It is curious to note that until the discovery of 

 thi- titi-rus of iln-m- animals hy Tyson, the vaguest 

 conjectures prevailed respecting iheir mode of 

 reproduction, it being even supposed by some that 

 tin lu-tus grew from the first attached to the nipple, 

 and consequently originated as a bud. 



t The name of Monotremata applied to these 

 animals, it may lie retmukcd, means mlh ./ r, nt . 

 they having a cloaca. 



duction. In concluding this rapid sketch, it 

 may not be out of place to introduce here a 

 few remarks upon the analogies existing be- 

 tweeii animal and vegetable reproduction. 



The seed of plants is generally regarded as 

 corresponding to the egg of animals. The 

 seed and egg correspond in being both the 

 residence of the germ or living part from 

 which the new organized body springs, and 

 also in both containing a certain quantity of 

 matter destined for the temporary nourishment 

 of the growing embryo ; but the germ is in a 

 different state in the seed and egg ; for while 

 in the egg none of the parts of the new being 

 are visible at the time of its separation from 

 the parent, the rudiments of the embryo are fre- 

 quently to be found, small but simulating in some 

 degree the plant, in the germ of the seed when 

 it is perfected, and before the commencement 

 of germination. The circumstances favourable 

 to evolution give rise to the development of 

 the embryo in both, but in the animal the 

 influence of the male conferring fecundity on 

 the egg makes no perceptible alteration in the 

 germ, while in the plant no part of the seed, 

 neither cotyledon nor germ, is formed unless 

 fecundation by the pollen of the male takes 

 place ; and the seed is not separated from the 

 ovary or place of its production until the 

 rudimentary parts of the embryo are already 

 sketched out. 



We have examples of non-sexual repro- 

 duction of plants among the Cryptogamia, in 

 which the new plant springs from sporules or 

 granules endowed with the independent vital 

 properties of the seed. 



The greater number of monocotyledonous 

 and dicotyledonous plants may be regarded as 

 hermaphrodite, as both the seeds and pollen 

 are formed on the same individual, while in 

 others the position of the sexual organs on 

 distinct individuals corresponds with the more 

 common arrangement in the animal king- 

 dom.* 



In different tribes of plants we also observe 

 examples of occasional propagation in a man- 

 ner different from the more common one by 

 seeds or sporules. Thus the buds and branches, 

 which are the means of their ordinary growth 

 and increase, may,when removed, be capable of 

 independent existence and give rise to distinct 

 plants, or even when still on the parent stock 

 may take root and grow anew. Some buds 

 separate naturally and are evolved in the man- 

 ner of seeds when placed in favourable circum- 

 stances ; and in a third class of instances sepa- 

 rated buds are preserved in the collections of 

 nutrient matter constituting the tuberous and 

 bulbous roots by which many plants are pro- 

 pagated. 



To complete the enumeration of the points 

 of analogy between animal and vegetable re- 

 production, it may be stated that there is the 

 same reason for believing in the spontaneous 

 generation of some of the Cryptogamic plants 

 as in that of Infusorial animals. 



* As in strictly Hermaphrodite, Monticious, and 

 Dioecious plants. 



