36 



OVUM. 



individuals from which the ovum derived its 

 origin : and that subsequently this individual, 

 or one or other of its successors, has formed in 

 connection with it, either internally or exter- 

 nally, and without sexual organs, a new progeny, 

 which may consist of one or of many indivi- 

 duals, which have each of them more or less of 

 the structure and properties of independent 

 animals, and which, however variable their 

 other organisation may be, present this in com- 

 mon, that they are sexually complete, and renew 

 the true generative act by the formation of 

 fecundated ova. In some animals it is the im- 

 mediate offspring of the individual developed 

 from the ovum which resumes the sexual func- 

 tion ; in other animals this offspring bears a 

 second brood, or a third, and even more suc- 

 cessive generations, before the return is made 

 to sexual reproduction. This process of non- 

 sexual production is, in some instances, very 

 analogous to external gemmation ; in some it 

 resembles transverse fission ; and in others it 

 proceeds from the interior of the parent body, 

 in a manner which has been called internal 

 gemmation, but which must be considered as 

 different from a true budding process, and 

 cannot, in a few words, be correctly charac- 

 terised. These deviations, therefore, are pe- 

 culiar in this, as compared with the mode of 

 reproduction in other animals; viz. 1st, that 

 the immediate product of development from 

 the ovum is not usually itself the producer of 

 ova, but that this function is delegated as it 

 were to the sexual individuals, which are die 

 products of its non-sexual generation; 2nd, 

 that it frequently happens that in place of one 

 individual only resulting from the development 

 of an ovum, several, and even a great multitude 

 of individuals are produced by the non-sexual 

 multiplication of the product of sexual genera- 

 tion ; and, 3rd, that while the several series of 

 individuals proceeding from the various suc- 

 cessive acts of production, may, in one sense, 

 be regarded as different stages of an animal 

 specifically the same, or are together necessary 

 to make up the species, yet their form, orga- 

 nisation, and modes of life are often so dif- 

 ferent, that many of them have frequently 

 been described as belonging to different species 

 and genera, or even to different orders and 

 classes of animals ; and, but for the know- 

 ledge now possessed of their close affinity, as 

 established by their common origin, would still 

 continue to be dissociated from each other in 

 the systems of the zoologist. 



The doctrine of alternating generation has 

 not, however, been admitted without reserva- 

 tion by some physiologists. In various parts 

 of his recent admirable work on General and 

 Comparative Physiology, and elsewhere*, 

 Dr. Carpenter has expressed his dissent from 

 the views of Steenstrup, both as regards tiie 

 existence of an alternation of a true gene- 

 rative process and the alleged nursing function 

 of one or more of the series of individuals so 

 produced; and seems disposed in some measure 



* In the Biitish and Foreign Medico-Chirur- 

 gk-al Keview, \ ol. i. and vol. iv. 



to undervalue that author's researches, con- 

 sidered either as original observations, or as 

 embodying a novel and important generalisa- 

 tion. Dr. Carpenter regards the phenomena in 

 question as analogous to, if not identical with, 

 those of metamorphosis rather than of genera- 

 tion ; and we are left to suppose that he does 

 not think the difference essential between such 

 metamorphoses as occur in one and the same 

 individual and those which result in the pro- 

 duction of a multitude of dissimilar indi- 

 viduals. According to this view, the new 

 animal produced by the non-sexual process is 

 the result of a process of development or 

 growth, and ought therefore to be regarded 

 as formed by budding or gemmation, rather 

 than by an act of generation properly so 

 called. In a recent paper on the subject of 

 Metamorphosis, Non-sexual Reproduction, 

 and Alternate Generation (Zeitsch. fur Wis- 

 sensch. Zool. June, 1851, p. 170.), Leuckart 

 has advocated somewhat similar views, endea- 

 vouring to refer all the instances of so-called 

 alternate generations to metamorphosis ; but 

 this obviously requires that we should change 

 the signification usually given to this term. 

 But the restriction of the word generation 

 to the sexual process of reproduction, though 

 it might be convenient and proper, were we 

 now to have to employ it for the first time, 

 seems somewhat arbitrary in this case, as it 

 is contrary to common practice, and ph}sio- 

 logists have long been in the habit of making 

 the distinction between sexual and non-sexual 

 generation. No new term has been suggested 

 applicable to, or descriptive of, all the pheno- 

 mena in question ; and I apprehend, that, 

 however desirable the change may appear, we 

 must continue to designate the process of 

 non-sexual production as one of " Genera- 

 tion" in its physiological sense, and the series 

 of new beings thus formed as so many 

 " generations" of individuals in the common 

 or vernacular sense of the term. As Pro- 

 fessor E. Forbes remarks, the alternation of 

 forms is admitted, but not the alternation of 

 generations. The bodies produced by one in- 

 dividual, if they assume new forms and move 

 about as separate and independent animals, 

 must be regarded as so many distinct indi- 

 viduals ; and if they are different, and if the 

 one produces the other (even though it may 

 be by a process of gemmation), we must ad- 

 mit that they belong to different generations. ' 

 The distinction between the formation of a 

 new individual from an impregnated ovum, 

 and that which takes place without the con- 

 currence of sexual organs, is one which, 

 unquestionably, all will feel disposed to re- 

 gard as most important ; but it still remains 

 undemonstrated that all the animal beings 

 which are of non-sexual origin are necessarily 

 formed by a process of gemmation analogous 

 to ordinary growth. It has already been 

 pointed out that the mode of their origin is, 

 so far as it has yet been ascertained, very 

 various ; and, at all events, in some of them, 

 there is a wide departure from that which we 

 have been accustomed to regard as an act of 



