OVUM. 



33 



arrived at maturity, and acquired the external 

 configuration and structure (though of smaller 

 size)^of the parent, was found to be possessed 

 of reproductive organs, while the original 

 animal had not acquit ed any. The first 



Fig. 29. 



Hijrianida fasciata. (From Milne Edwards.) 



Twice the natural size. At the posterior part of 

 the body are seen six young, produced between the 

 caudal and the next joint in succession, from 1 to 6. 



formed was situated farthest back, and re- 

 mained for the time attached to the original 

 caudal joint, and the others followed in suc- 

 cession before it, the last produced being 

 attached to the terminal joint of the parent 

 body ; and each newer individual presented a 

 less developed structure than the preceding 

 one. In the animal observed by M. Ed- 

 wards, the anterior or youngest individual 

 had only ten rings, the second had fourteen, 

 the third sixteen, the fourth eighteen, the 

 fifth twenty-three, and the last, or caudal one, 

 thirty rings. It would appear, therefore, 

 that the new individuals take their origin 

 from the last joint of the parent Annelide. 

 The observations of M. Edwards farther 

 make it appear that the process of develop- 

 ment and multiplication of the segments in 

 each of the new individuals is the same as in 

 the young Annelide first formed from the 

 ovum ; that is, the embryo is at first without 

 segments or rings, the head and caudal part 

 existing alone, and the joints being gradually 

 formed between them, and in succession, from 

 the posterior of the segments previously pro- 

 duced. 



These phenomena cannot fail to recal to 

 our recollection the production of sexual 

 individuals by a non-sexual process analogous 

 to gemmation from imperfect parents or nur- 



Supp. 



sing stocks; and as Mr. Owen has remarked*, 

 " Since the individuals so propagated alone 

 acquire the generative organs, an alternation 

 of generations may here be affirmed of such 

 species; the oviparous individuals producing 

 eggs from which the gemmiparous individuals 

 come, and these, in their turn, reproducing 

 the oviparous individuals."-}* 



But it is to be observed, that in many 

 others of the Annelida, the generation is of 

 the ordinary kind, or consists in the produc- 

 tion of sexual individuals, by their direct or 

 metamorphic development from the ovum. 



Insecta. Aphides. A remarkable example 

 of a similar modification of the reproductive 



Fig 30. 



Production of Aphides. 



A. (After Owen.) Diagrammatic representation 

 of the succession of generations of Aphides, from the 

 fecundated ovum o, the first embryo e, the suc- 

 cessive non-sexual progenies, g to g (of each of 

 which only one individual is represented), to the 

 male and female insects, m and/. 



B. (After Leydig.) Enlarged view of the cham- 

 bers of one of the ovarian oviducts of a viviparous 

 Aphis. In the uppermost chambers are seen the 

 fine nucleated cells, of which one in 1' and 2', larger 

 than the rest, descends ; and in 3, 4, and 5, are seen 

 the changes of this and other granular and cellular 

 blastema, from which the new. individual is formed. 



* Lectures, 1849, Med. Times, vol. xx. p. 83. 

 t At the same time it ought to be mentioned in 

 connection with the above, that, according to some 



D 



