404 JOHN BEARD, 



dicated, Metazoan development may turn out to be, like metaphytic 

 reproduction, a form of antithetic alternation of generations. 



Owing largely to a disastrous pursuit of the will o' the wisp of 

 recapitulation, our knowledge of the laws governing the embryo- 

 logy of animals lags far behind what the botanists have already 

 gleaned regarding those of plant-development. Among all but the 

 lowest plants antithetic alternation is now clearly established, and 

 the brilliant morphological researches of Bower ^) need only be men- 

 tioned as illustrating recent remarkable advances in this field. Whatever 

 else the embryologist may do, he cannot conscientiously shut his eyes 

 to the patent fact that alternation of generations of this kind does 

 obtain in some animals, although, at the moment, he may fail to re- 

 cognise the universality of its presence in the Metazoa. 



But science moves apace, and the day may dawn when alter- 

 nation of generations will no longer be viewed as the exception — 

 when it will have taken its position as the law of development. 

 Then, and not until then, we shall perceive more clearly the funda- 

 mental unity, which underlies organisation and development in the 

 animal and vegetable kingdoms, — a unity perhaps conditioned by a 

 similar marine pelagic origin. 



Spore-formation and a spore-producing generation would, in the 

 tacit opinion of practically every embryologist, appear to be quite 

 absent in the Metazoa, except, perhaps, in a few special and doubtful 

 cases, like the Dicyemidae and the Trematoda. 



Why this spore-formation and the corresponding spore-bearing 

 generation should have been suppressed, or disguised, in the Metazoa 

 — assuming that they once obtained — are problems for the earnest 

 consideration of the embryologist. If one should recognise with the 

 writer that antithetic alternation may be regarded as an universal law 

 of Metazoan development, there would be a strong temptation to cite 

 Bower's researches and results on apospory in certain ferns as giving 

 an indication of a possible way in which spore-formation became 

 suppressed in animal development. His results remind one in a striking 

 fashion of the way in which the mature form arises on a larval 

 foundation in more than one Invertebrate. 



These few remarks on an intensely interesting but difficult subject 

 may bring home to the reader a conviction that the bare fact of the 



1) BowEK, R 0., Studies in the morphology of spore-producing 

 members. — Equisetineae and Lycopodineae, in: Phil. Trans. R. Soc. 

 London, V. 185, 1894. 



