Jax. 1902.] BOTANICAL SOCIETY OF EDINBURGH 129 



What Xussbanm rightly insisted upon was the early 

 appearance of the germ-cells in the sexual generation of 

 animals, i.e. in the embryo before this had undergone 

 histological differentiation. In urging this Xussbanm 

 really took up a very moderate attitude. To refute his 

 argument from the botanical side, it is necessary to 

 compare the conditions in the corresponding generations 

 in the two kingdoms — that is, to place the embryo and the 

 prothallus together, not the embryo and the sporophyte. 

 It should also be pointed out that even now the early 

 history of the germ-cells of " most animals " has as yet 

 been very inadequately investigated. Where it has been 

 traced back to the farthest possible point, there a very 

 early origin has been invariably made out. This is now 

 so in Jfoina, Cyclops, Ascaris, Strongylus, Cccidomyia, 

 Chironomus, Sagitta, Pludanrjium, Lerncea, Micromdrns, 

 Scorpions (Brauer), several insects (Heymons), some 

 sponges (Maas), and Cephalopoda (V. Faussek), and, 

 lastly, in Pristiiirvs (Eabl), Scyllium, and JRaja. 



Hitherto the apparent phenomena in the Yertebrata 

 stood in the way. Here even a segmental origin of the 

 " sexual cells " had been recorded in relatively late stages. 

 This is, however, only one of the ever-recurring instances of 

 the earliest observed appearance of a thing being taken to 

 represent its first origin. This is only permissible in 

 embryological research, when an earlier origin is absolutely 

 out of question. 



From a fair acquaintance with the embryological litera- 

 ture treating of the germ-cells and their origin, the writer 

 must maintain that there is really no reliable evidence 

 pointing to the very late appearance of the germ-cells 

 in any single case. On the other hand, there is a steadily 

 accumulating body of very strong testimony in favour of 

 their very early separation off in many different divisions 

 of the animal kingdom. Even the case of the Hydkoid 

 POLYPES cannot be cited in disproof, for Weismann's own 



vivum ex ovo,' there thus already lay the continuity of the embryonic 

 substance. This is, at the same time, in eternal youth and organic 

 immortality the substance of the uniceUular organism?, which, repro- 

 ducing by fission, are used up in one another without residue." — F. 

 Noll, iii Strassburger's " Lehrbuch der Botanik," 2te Autl, 189."), 

 pp. 208, 209. 



