OVUM. 



39 



with the development of flowers. It is not 

 without considerable interest, that the same 

 conditions as to temperature, season, supply 

 of nourishment, &c., seem to determine the 

 one or the other kind of production in both 

 the animal and the vegetable bodies. Many 

 botanists regard the plant as an assemblage 

 of individuals; and zoologists are for the most 

 part agreed as to the distinct individuality 

 of the parts united in a compound polype. 

 But the tendency to spontaneous separation 

 of these individuals, especially in their sexual 

 form, is very frequently exhibited in the 

 animal kingdom, while it is rarely, if ever, 

 met with among plants ; and among the 

 polype tribes, as well as in other examples 

 of alternate generation, the striking dif- 

 ference of form, structure, mode of life, 

 and functions, of some of the sexual indivi- 

 duals developed by non-sexual generation, 

 seem to warn us against extending the compa- 

 rison farther than the admission of the general 

 analogy above adverted to, or, at all events, 

 precludes us in the mean time from drawing 

 any arguments as to the nature of animal pro- 

 duction from that which is as yet only imper- 

 fectly understood in the vegetable kingdom.* 

 These considerations raise another ques- 

 tion on which recent writers are at issue in 

 regard to the theory of Alternate Generations, 

 viz. whether the various animal bodies formed 

 by the non-sexual process within one act of 

 sexual generation are to be regarded as so 

 many individuals composing the species, or 

 whether they are to be considered only as the 

 different states of one and the same indi- 

 vidual. I have abstained from entering 

 directly on the discussion of this question, 

 from the desire to avoid the confusion which 

 is apt to arise in it from the use of terms in 

 other than their usual significations. In re- 

 gard to connected animal forms, such as those 

 which coexist in a Compound Polype, less 

 difficulty might be felt than in those instances 

 in which a complete separation of the progeny 

 from its producer has taken place ; but it 

 seems to require a greater departure from the 

 ordinary signification of a common term than 

 is warranted by our present imperfect know- 

 ledge of the phenomena, arbitrarily to de- 

 termine to regard as merely one individual all 

 those bodies which may be formed by a non- 

 sexual process from the product of a single 

 ovum, notwithstanding the great variations in 

 their structure and mode of life, and the com- 

 plete separation and apparent independence 

 to which they may attain. It is unquestion- 

 ably important to acknowledge the integrity 

 and permanence of the species as maintained 

 in the midst of all these variations by gene- 

 ration from an ovum ; but there does not 

 seem to be any obvious impropriety in the 

 instances in question in regarding the species 

 as made up of individuals differently con- 

 stituted among themselves, and produced one 

 out of another by a non-sexual process. The 



* For farther remarks on this subject the reader 

 is referred to an account of vegetable production, 

 under the Article VEGETABLE OVUM. 



term Zooid suggested by Huxley, or Zoonite 

 previously employed by Milne Edwards and 

 some other French authors, or any such term 

 agreed upon as implying a relation of affinity 

 among the various bodies included in one act 

 of true sexual generation, may perhaps re- 

 move some of the ambiguity; but I confess I 

 do not think the present state of the inquiry 

 warrants the total abnegation of individuality 

 to the various animal bodies produced in the 

 non-sexual manner.* 



In reviewing, then, the whole subject of 

 Alternate Generation, it seems to be equally 

 premature to refer the whole of the pheno- 

 mena included under this term, which may 

 hereafter be discovered to be very various in 

 their nature, to a simple process of gemmation 

 or individual development, or to attribute 

 them to the existence of certain powers, such 

 as a germ-force or spermatic power, remaining 

 in certain germ-cells, or to reject altogether 

 the hypothesis of Steenstrup of Alternate 

 Generations, which indeed is little more than 

 the expression of the course of the observed 

 phenomena ; until we shall know more exactly 

 the minute structure of the germ from which 

 a bud arises, and the difference between that 

 and the germ of an ovum, and until we shall 

 be more fully acquainted with the whole 

 structure and series of changes of the various 

 animal forms that have been the subject of 

 consideration in the preceding section. 



We regard it, therefore, as more consistent 

 with the actual state of our knowledge of the 

 facts to describe the phenomena of Alternate 

 Generation as a peculiar mode of existence 

 belonging to some of the simplest kinds of 

 various classes of Invertebrated animals, 

 which seems to have especial reference to the 

 preparation of the sexual organs ; and of this 

 nature, that the animal immediately developed 

 from the fecundated ovum does not usually 

 arrive at sexual completeness, but has formed 

 from it, by a non-sexual process of production, 

 another individual of a different form, or a 

 succession of them, which finally attain to 

 sexual completeness, and produce the fecun- 

 dated ova that originate the generative cycle ; 

 and the effect of which is, to render two or 

 more successive generations of dissimilar ani- 

 mals necessary to the completion of the 

 species to which they belong. 



* Some acute and interesting remarks by Mr. 

 Huxley on this subject will be found appended to 

 a sketch of J. Muller's discoveries on the Echino- 

 dermata, in the Annals of Natural History, 1851, 

 vol. vii. p. 1. I would also refer at this place to 

 the Lectures of M. Agassiz on Comparative Em- 

 bryology, Boston, 1849, as presenting a most en- 

 gaging view of the influence which the study of 

 the metamorphosis of animals, along with the 

 history of alternate generations, must exercise on 

 the systematic views in Zoology and Comparative 

 Anatomy, and I also take this opportunity of refer- 

 ring to some remarks by Mr. C. Spencer Bates in a 

 paper on the Development of the Cirripedia, in the 

 Ann. and Mag. of Xat. Hist, for 1851. vol. viii. p. 

 331. for a statement of the relations subsisting be- 

 tween the various forms of animals considered in 

 their sedentary and free states, either in individual 

 species or in different 'genera or families of the 

 various classes of animals. 



D 4 



