1890.] 115 [Ryder. 



in the flowers, and such may have been the further effect of the new 

 diet upon insect life as to be directly responsible for the evolution of 

 those wonderful insect communities developed amongst the honey-lov- 

 ing hymenoptera or bees. The further consequences of entomophilous 

 traits developed by plants must react in other ways, probably through 

 epinasty and hyponasty, in modifying the shapes of flowers, while pro- 

 tandry, a natural consequence of the earlier maturation of the andrce- 

 cium, as a lower whorl of the flower, would eventually tend to establish 

 cross-fertilization, through insect agency, as an imperative necessity, and 

 not wholly, perhaps, because cross- fertilization meant the production ot 

 a more vigorous offspring. 



The gradual evolution of sexuality by slow stages in plants is now so 

 well understood, that it is not necessary to enter into the details which 

 may be found in any standard botanical text-book. It is sufficient to indi- 

 cate that the transition from asexuality to female macrogonidia and 

 male microgonidia is effected by mere differentiation of cells as re- 

 spects their size. From naked oospores to carpospores is the next step, 

 with microscopic flagellate male elements. Finally, the prothallus ap- 

 pears, first, with both oospheres and antherozoids ; then the prothalli 

 themselves become distinguished as small male and large female ones ; 

 then the female prothallus is no longer at once detached, but becomes 

 covered in, while the minute male prothallus still dehisces, but finally be- 

 comes partially parasitic upon the stigma where it vegetates and throws 

 out a hollow process, which serves to convey the now highly modified 

 antherozoid to the ovicell. The prolonged adherence of the female pro- 

 thallus to the parent axis enables the next important step to be taken in 

 the evolution of the seed containing a viviparously produced embryo pro- 

 vided with a store of nutriment and protective envelopes. 



In this way the superimposition of more and more successful means of 

 reproduction seems to have occurred in plants, tending also to secure the 

 final victory of the phanerogams over all other rivals in the struggle for 

 existence, largely through the evolution of viviparity as supposed above. 

 How much of this success was due to the principle of overgrowth or cumu- 

 lative integration, which made rapid, continuous assimilation and growth 

 possible through the evolution of a mechanical supporting system, is 

 hard to tell, but it doubtless was quite as important a factor as natural 

 selection itself. 



Similar conclusions are borne in upon the zoologist in a stiidy of 

 the reproductive processes in the animal world. From asexual frag- 

 mentation and consequent multiplication, the advance to larger and 

 smaller, or female and male elements, was a gradual one, with or without 

 hermaphroditism. Then came hermaphroditism with large female and 

 small male germs, then maleness and femaleness, as characterizing dis- 

 tinct individuals of the same species. Finally, protective processes were 

 developed, accompanied by ovulation, followed by parental care, such as 

 incubation, nidification, gestation with or without placentation, and at 

 last, in the highest forms, lactation was developed. 



