XVII] PREVALENCE OF HOMOPLASY 343 



matched in Algal types, and often in such as are systematically quite apart 

 from one another. They probably illustrate a wide polyphylesis in somatic 

 development of organisms at large. But it is noteworthy that a departure 

 from the filamentous state, and an early substitution of the massive soma, is 

 particularly likely to occur under the biological conditions attending life upon 

 land. In fact the elimination of the filamentous stage would be almost a 

 biological necessity in terrestrial plants: and this is probably the reason why 

 evidence of its existence is so often absent, or effectively disguised, in the 

 Archegoniatae. 



In all such comparisons between large divisions of the Vegetable Kingdom 

 the probability of far-reaching polyphylesis should be constantly kept in view. 

 The prevalence of homoplasy within the nearer circles of affinity is becoming 

 clearer every day. The Filicales show it among themselves in very high 

 degree in external form, in anatomical structure, and in soral and sporangial 

 characters. It is evident also in their gametophyte-generation. It appears 

 on comparison of the Filicales with other Archegoniatae. The Algae also 

 show homoplasy in high degree between their own Red, Brown, and Green 

 Series. All sexually produced organisms start from the egg, and each must 

 attain its adult form by progressive development from that simple source. 

 Is it not then probable that homoplasy should produce forms and structures 

 in Algae and Archegoniatae which, though'similar, are analogous and nothing 

 more ? The tracing of analogies between the form, structure, and propagative 

 organs of plants is an easy and a seductive occupation. But to put any more 

 direct interpretation than analogy upon the similarities which they, and 

 especially their higher forms, show could only be admitted after close 

 comparison of sequences of proved relationship. It is only in this way that 

 analogies can be raised from the atmosphere of vague surmise to the level 

 of scientific hypothesis(3i5). Hitherto such sequences have not been demon- 

 strated between the Algae and the Archegoniatae. It still remains an open 

 question whether points of contact are to be found between the Archegoniatae 

 and the Red, the Brown, or the Green Algae, though analogies may be traced 

 with representatives of each of these distinct series. This in itself should 

 give pause to unrestrained theorising. But whatever real relationship there 

 may be between Algae and Archegoniatae, indications of it should be sought 

 among lowly and generalised forms rather than among the more specialised 

 Algal types. The comparative analysis of both the generations of the Fili- 

 cales makes it seem probable that their Algal progenitors may have been 

 still filamentous at the time when they essayed the transition from water to 

 life on land. 



That transition has involved, in one way or another, the encapsulation 

 of the embryo(3o6). Its protection within such an organ as the archegonium 

 was a matter of the highest importance for successful sub-aerial life. Hence 



