518 REVIEWS— THE GENETIC CYCLE IN ORGANIC NATURE. 



and that the products of the former differ more or less in their conformation- 

 from the organisms budded off in the latter. 



Hence, as both forms must be taken into account to complete our idea of the 

 perfection of the species, it has been proposed to term them zooids in the case 

 of animals, and phytoids in that of plants, as indicating that any one of them 

 is not so much a complete animal or plant in itself, as a fragment or fractional 

 part of one — the whole series, considered as a specific unit, rather than any one 

 among the successive links of which it is made up, answering to our idea of 

 individual completeness, as this is drawn from the higher animals, in which like 

 seems always to produce like. 



In confirmation of such a view, it is noticed that in not a few cases these 

 fractional phytoids and zooids really remain in organic union for life — making 

 up an arborescent form — like what we call a polypidom in animals, which is 

 readily recognized as being in its entireness the individual representative of 

 the species. 



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Though we may allow so much in common in these cases of " alternation," as 

 is involved in the occurrence in all of a periodic diversity of derived forms, 

 there are yet — as was pointed out in the introductory chapter — great variations 

 among them, as far as the relations are concerned in which the budding process^ 

 stands to the sexual act, and to the full development of the specific type- 

 relations depending on the period of the life-history of the species, at which the 

 act of gemmation is interpolated in the genetic cycle. The contrast lies especially 

 between the cases in which the alternation of form is due to zooids being budded 

 off in the Protomorphic stage of the life-history — that is, during the early 

 progress of germinal development — and those in which it arises from the 

 detachment of gemmae in the fully developed or typical phase, as a preliminary 

 step so the evolution of reproductive organs — the latter zooids belonging to the 

 Gamomorphic stage, or that of sexual maturation. The two classes — as has 

 been already observed — differ widely in their structure and relations. In the 

 one case they are the primary products of impregnation, precursors of the 

 perfect form, and without sexual characters — in the other derivative, and 

 with distinct sex. Zooids of both kinds, indeed, may have certain organs 

 superadded, varying in their nature and completeness with the circumstances 

 of their life as independent beings. In those of the protomorphic stage, 

 the adventitious organization probably does not go beyond the development, 

 externally, of cilia, or of a contractile integument for locomotion, and internally, 

 of a rudimentary digestive apparatus ; but in many gamomorphic zooids, both 

 the locomotive and alimentary systems may be rather highly organized, and the 

 whole structure occasionally larger and more complex and elaborate than that 

 of the parent stock. On the other hand, such is the structural degradation of 

 some zooids of both kinds, that they might readily pass for mere proliferous 

 cysts or egg-sacs. This variability in the kind and extent of organization 

 proves of itself its adventitious nature, and shows it to be of no value as a 

 distinctive feature. The real points of distinction are those before referred to— 

 their position in the genetic cycle, and their gemmiparous or sexual character in. 



