378 ANNUAL OF SCIENTIFIC DISCOVERY. 



mated an opposite valve taken at Provincetown, Mass. At Hakocladi, 

 Japan, the arctic fauna exists, and the shells of this coast are found; whilst 

 at Siraoda the shells are those of the China seas. Birds can traverse the 

 ocean in the northern regions where the continents approach each other, but 

 it is a question if mollsuca can travel such distances. 



ON PARTHENOGENESIS. 



This word, as its derivation implies, signifies the production of young by 

 the female sex alone, as in the Aphides, or common plant lice, in which gen- 

 eration follows generation, for a dozen or more, without renewed intercourse 

 with the other sex. 



There are two modes of generation well known in plants and animals, 

 one by true eggs, the other by buds without eggs. The plant kingdom is 

 known to be full of both processes. The bud from a branch, developing 

 regularly its leaves, and capable as it often is of propagation, where separa- 

 ted, as well as when united to the original stem, is one variety of propaga- 

 tion by buds. The bud originating as a bulb at the axils of the leaves and 

 branches, which drops off, and on finding soil, produces a new plant, is an- 

 other variety of growth by buds. As each plant from such a bulb or bulbel 

 will produce its crop of bulbels, propagation may be continued on apparently 

 indefinitely, without necessary intervention of true flowers. 



The Animal Kingdom, in its inferior departments of the Radiates and 

 Molluscs, exemplifies the same method of propagation. The young polyp 

 may grow from the side of the old, and be persistent, like ordinary buds of 

 plants, but becoming an independent individual if cut off; or, in other cases, 

 it may drop otf on reaching towards maturity, and thus acquire indepen- 

 dence, and so become the parent of a new zoophyte. Thus far the two king- 

 doms have long been known to be alike in reproduction. The bulbels of the 

 plant are not like true seed in structure, neither are the bulbels of the Cam- 

 panularidaj. There is not the germinal vesicle with its germinative spot. 

 The development is simply germination. The analogies between plants and 

 animals, it may be stated, go still further; for as plants produce leaf buds, 

 and then flower buds, and then flower buds in which sexual organs and seed 

 are developed, so some Medusas (Tabularidae) bud out polyps to make the 

 branching stems, and afterwards bud out Medusae to develop sexual or- 

 gans and ova; these Medusae (as occasionally happens with the flowers of 

 plants) separating and becoming free from the stalk that produces them. 

 Moreover, it is now understood that the so-called alternation of generation is 

 nothing more than the successive states exemplified in plants, of the embryo, 

 incipient leaf bud, opened leaf bud, flower bud, and flower, all of which are 

 often widely diverse in forms. 



It was in view of such facts as these that the late Dr. Burnett undertook to 

 determine the nature of the process of continual nonsexual propagation in 

 the Aphides; and his conclusion was, that the egg-like bodies, developed in 

 clusters within the producing Aphis, were of the nature of buds, and not 

 true ova, agreeing in this with Dr. Carpenter; and that the whole was anal- 

 ogous to the budding process. "The germs," he says, "have none of the 

 structural characteristics of eggs, such as a vitellus, a germinative vesicle 

 and dot; on the other hand, they are at first, simple collections, in oval 

 masses, of nucleated cells." He also refers to the same kind of origin, the 

 so-called hibernating eggs of Daphnia among Crustacea, Lacinularia among 



