ADDRESS. lxxix 



■within the parent body, without, however, direct union or continuity of tissue, 

 till the embryo has attained some advancement, as in the well-known case of 

 tho seeds of a phanerogam ; but there are many varieties in the mode of its 

 disposition among the lower plants. 



A remarkablo exception to the more direct relation of the process of ferti- 

 lization to the formation of the new individual or embryo occurs in some 

 plants, simulating in some respects that kind of variation in animal reproduc- 

 tion which has been named alternate generation. A well-known instance of 

 this is observed in the Vascular Cryptogams. The prothallium of the Ferns, 

 for example, results from the development of so-called spores or unicellular 

 biids, which are familiar as being formed in small capsules on the lower leaf- 

 surface ; and in this prothallium, when it has reached a certain stage of vege- 

 tation, there are formed the archegonia, containing the oospheres or germ- 

 cells, which are fertilized by the moving ciliated particles developed in the 

 cells of the antheridia, the process resulting in the production of a new 

 spore-bearing frond or fern-plant. 



Recent researches have also called attention to the remarkable arrange- 

 ments in many Phanerogamic plants for the prevention of fertilization of the 

 pistils by pollen from the same flower, or even from the same plant. In the 

 latter case this is effected by the separation of stamens and pistils in different 

 flowers. In the former case, where both organs occur in the same flower, 

 the adaptations, whether of a mechanical or of a physiological character, by 

 which self-fertilization is prevented, as ascertained by numerous recent inves- 

 tigations (among which those of Darwin are most conspicuous), are of the 

 most varied and often the most complicated kind. 



Let us now turn to the consideration of the Development of Animals ; 

 and let me say in the outset that it will be necessary for me to confine my 

 remarks chiefly to the higher or vertebrated animals, and to certain parts 

 only of the history of their development — more particularly the structure and 

 formation of the ovum or egg, some of its earlier developmental changes, and 

 the relation of these to the formation of the new animal. 



I cannot enter upon the consideration of this topic without adverting to 

 the very recent acquisition of some of the most important facts upon which 

 this branch of knowledge is founded ; and I feel it to be peculiarly appropriate, 

 in the year of his death, to refer to a Biologist whose labours contributed 

 more powerfully than those of any other person to give to animal embryology 

 the character of a systematic branch of science, and to whom we owe some 

 most important original discoveries — I mean Karl Ernest von Baer of 

 Konigsberg, St. Petersburg, and Dorpat. 



Of observers who, previous to Yon Baer, were mainly instrumental in 

 preparing the way for the creation of a more exact modern science of embry- 

 ology only two can be mentioned, viz. Caspar Frederick Wolff of St. Peters- 



