j\I. N. Prin<^slit'iin mi fhi- PairliKj of Zuofiporcft. 277 



mass at the fore end of the brood-spheres, tlie canal-cell of 

 the higher Cryptogams, and the filamentary process {Faden- 

 Apparat) in the embryonic vesicle of Phsenogams. 



Those cases amongst the Algne where, as in (Echgoniinn 

 and Pandorinn, the entire mass of the brood-sphere, including 

 the whole of the germ-spot, is em])loyed in the formation of 

 the embryo, are introductory to the procreative act in Vaii- 

 cheria, where a portion of the germ-spot is pushed away and 

 cast off before impregnation ; and through Vaucheria and the 

 analogous formative process in Coleocha'te the passage is 

 direct to the canal-cell and the filamentary process. Thus the 

 zoospore appears as the ground-form of the embryonal rudi- 

 ments in the vegetable kingdom ; and in the formation of 

 these there is a striking analogy to the phenomena which, in 

 the formation of the embryo in animals, are distinguished as 

 total and partial segmentation. 



It may also be worth Avhile to call attention to the fact tliat, 

 in comparing embryonic vesicles and zoospores, the position of 

 the brood-sphere before impregnation throws light upon the 

 direction of the root of the embryo in those plants in which 

 an embryo is the result of the procreative act, inasmuch as 

 the gemi-spot, which from CEdogonium up to the Phajnogams 

 is without exception turned towards the sexual aperture, cor- 

 responds, as the zoospores show, to the /oof of the germ. 



But it being the fact (as is shown by the spermatozoids of 

 CEdogonium and Pandorina) that the differences in fomi which 

 have been hitherto attemjited to be established between sper- 

 matozoids and zoospores have only a relative value as modifi- 

 cations of the same primary form, it will follow that the form 

 of the zoospore, in which even the oldest observers noticed a 

 connecting link between the vegetable and animal kingdoms, 

 may be recognized as the ground-form of all reproductive 

 bodies in plants, and thus an embrj^ological unity may be 

 distinguished in the vegetable kingdom, unless the mode of 

 copulation of the Fhrideff and the Fungi should turn out to 

 be very divergent, as to which further observations must 

 decide. 



It is probable that a number of ill-understood phenomena 

 and of unintelligible contradictions of reliable botanists as to 

 the form and colour of microgonidia, as to the number of their 

 cilia, as to their behaviour after the cessation of their mobility, 

 and, lastly, probably, as to double spores, may be fully ex- 

 plained by the supposition of the process of pairing. 



It should now be the object of those observers who are oc- 

 cupied in investigating the development of Algse to look for 

 the phenomenon of " pairing," or for motile brood-spheres, in 



