944 



SCIENCE. 



[N. S. Vol XII. No. 312 . 



that reproduction and the combination of 

 idioplasms are separate phenomena. 



To emphasize the difi'erence between the 

 two processes suppose we consider fertiliza- 

 tion as a complicated morphological process, 

 and reproduction as something which can be 

 accomplished in another way. The first 

 serves to unite substances which possess a 

 stable organization. The second, like all 

 cell-divisions, merely changes a physiolog- 

 ical condition of equilibrium. Partheno- 

 genesis is an example of how the power of 

 development may be present in the absence 

 of fertilization. My own view of this phe- 

 nomenon is that the necessary reciprocal 

 -.elations of nucleus and protoplasm are in 

 8ome way established and division ensues. 

 The so-called fertilization of non-nucleated 

 egg-fragments seems to me an analogous 

 case which no one who cvusMrrs the nuclei 

 the bearers of the idioplasm can call true 

 fertilization. It is much more likely that 

 the necessary reciprocal relation is estab- 

 lished by a fusion of the egg-plasm with the 

 plasma of the spermatozoan, in which event 

 we should be dealing with a counterpart of 

 parthenogenesis. 



It would therefore be entirely conceivable 

 that the conditions necessary to division 

 could be produced in ripe unfertilized eggs 

 by chemico-physical influences. Loeb's ob- 

 servation that the eggs of sea-urchins {Ar- 

 bacia punctulata) develop to plutei if they 

 have been previousl}' exposed to the ac- 

 tion of a certain salt solution, raises no 

 theoretical objections to this view. I have 

 myself succeeded in making unfertilized 

 eggs develop after treatment with chemical 

 reagents (strychnine), although they pos- 

 sessed the power of development to a lesser 

 degree. 



It would be of the greatest interest to 

 trace the sexual reproduction of the Meta- 

 zoa from its origin in the reproduction of 

 unicellular forms. Unfortunately the solu- 

 tion of this problem is made the more dif- 



ficult by the wide gap which separates the 

 Protozoa and the Metazoa. The Mesozoa 

 are not suitable for our purpose. Their de- 

 velopment is not sufiBcientl^' known and 

 has probably been modified by the entire 

 class having become adapted to a parasitic 

 life. Nevertheless the investigations upon 

 the best known Dicyemidae give strong in- 

 dications that their reproduction still fol- 

 lows the method of the Protozoa. The en- 

 doderin of Dicyema produces reproductive 

 cells which in many cases yield young ani- 

 mals directly, in others probably after pre- 

 vious fertilization. The first process serves 

 for auto-infection ; the last probably occurs 

 when the parasite would be carried to a 

 new host. The first is known in an en- 

 tirely arbitrary way as parthenogenesis, 

 when the criterion of parthenogenesis (loss 

 of fertilization) is not proved. It evidently 

 corresponds to the so-called asexual repro- 

 duction of the Protozoa. When their mul- 

 ticellular condition and the modifications 

 which it entails are considered the develop- 

 ment of the Dicyemidse seems to admit of 

 a very close comparison with the develop- 

 ment of the likewise parasitic Coccidise and 

 Hsemosporidiie. 



Plants offer a much more favorable field 

 for the solution of this problem than ani- 

 mals because they exhibit many forms mid- 

 way between the uni- and multicellular 

 organisms. In the multicellular Algse 

 there are two kinds of reproduction: (1) 

 asexual, by means of spores and (2) sexual 

 by means of gametes. Both have in com- 

 mon the fact that single cells separate from 

 the cell community and grow up into new 

 plants. In the first case it is each time a 

 single cell for itself, in the second a cell 

 which has previously copulated with one of 

 a different stock. The dilFerence between 

 spores and gametes is often quite pro- 

 nounced both in their structure and their 

 method of development. In other cases the 

 anatomical and developmental difi'erences 



