No. 550] NOTES AND LITERATURE 



029 



permanent closure, the infundibulum and adjacent nerve tissues in 

 vertebrates representing the remnants of the old stomodeum with its 

 nerves and ganglia. . . .* (12) The process of gastrulation in verte- 

 brates and arachnids is confined to the procephalic lobes, in the place 

 where at a later period the primitive stomodeum appears. The so- 

 called "gastrulation" of vertebrates and arachnids is an entirely 

 different and independent process, that is, the process of adding by 

 apical or teloblastic growth a segmented, bilaterally symmetrical body to 

 a primitive radially symmetrical head. (13) The arachnids resemble 

 the vertebrates in more general ways, as in the minute structure of 

 cartilage, muscle, nerves, digestive, and sexual organs. (Pp. xvii and 

 xviii of the Introduction.) 



None of the statements in this list, either those quoted or those 

 not quoted, bring out clearly one of the most striking features of 

 the theory, namely, the supposition that the ventral surface of 

 the arachnid became the dorsal surface of the vertebrate. This 

 is well shown by several series of figures, as, for instance, that 

 on page eight, of imaginary arthropods and vertebrates with 

 creatures intermediate between them. 



During the twenty years and more that the theory has been 

 before zoologists it seems to have won very few adherents; in- 

 deed, to have had little influence on biological thinking of any 

 sort. Nor does it seem probable that this final marshaling of 

 the evidence will accomplish much more as regards the main 

 contention. So far are we still from certainty as to exactly how 

 and when the back-boned animals originated that even the prob- 

 able evidence toward such knowledge is not great. Indeed, if 

 one will consider fully the nature and difficulties of the prob- 

 lem he will see that the chance of ever reaching certainty is 

 almost nil. 



What would constitute a demonstration of the parenthood of 

 vertebrates? Obviously the most indubitable proof, that of 

 direct observation, is out of the question. The "supreme canon 

 of historical evidence that only the statement of contemporaries 

 can be admitted," must, in the nature of the case, be completely 

 ignored here. The best chance of reaching a demonstration is 

 m finding a series of fossil animals intermediate between some 

 unmistakably primitive vertebrate and the assumed ancestor, 

 containing no gaps great enough to raise serious doubt in the 

 mmd of any competent authority as to the genetic relationship 

 'Number nine in this list is absent in the text. Numbers 10 and 11 are 

 Purposely omitted in the quotation. 



