592 PROFESSOR MARCUS HARTOG. 



Ecliinodermata, the very group on which the above experi- 

 ments were chiefly tried. Again, in many lower organisms 

 whose pairing-cells are not differentiated into sperm and 

 oospherO; but are similar, should fusion fail to occur at the 

 right moment, it is not only impossible, but needless ; for the 

 single cell will develop iiidividnally, its product taking the 

 same course as would have done the product of a fusion (e. g. 

 Ulothrix, Spyrogyra). Such development, known since 

 the eighteenth century, had received the name of "partheno- 

 genesis." The process is clearly identical in nature with the 

 development of non-pairing resting-cells, such as the resting- 

 spores of Fungi, Algae, and many Protozoa, to which the term 

 " germination " is applied. This same term is also given to 

 the starting into development of such multicellular bodies 

 as the seeds of flowering plants, and their bulbs and tubers, 

 and similar bodies in higher animals, like the statoblasts of 

 Polyzoa. For germination to take place favourable external 

 conditions are sometimes needed ; while in other cases, as 

 with the seeds of the mangroves, there is no pause, and the 

 seed develops as soon as formed. The renewed growth after 

 rest, whether of spores or of seeds, single cells or cell-masses, 

 appears to be due first to the formation of ferments that can 

 dissolve the intra-cellular reserves; and next to the conditions 

 that favour the action of such ferments, and the consequent 

 growth of protoplasm at the expense of the reserves rendered 

 available by digestion. We may henceforward regard all 

 such starting into growth as "germination," reserving the 

 term " parthenogenesis " for the special germination of cells 

 that normally (or rather commonly) are capable of a fusion 

 process with another pairing cell ; in other words, "partheno- 

 genesis " is the direct " germination" of a potential gamete. 

 On the other hand, the development of the resting-cell (of 

 which to us the Metazoan egg is the most familiar type) and 

 the process of cell-fusion are by no means invariably 

 associated together in Nature. True, they are so connected in 

 the cases most familiar to us, but in the bird's egg itself the 

 development of the germ is arrested on laying, and the 



