82 VERTEBRATE ZOOLOGY 



recognition; although the evidence, especially in Professor Pat- 

 ten's book, is based upon an admirably executed piece of re- 

 search." 



As Lull has intimated, it is highly improbable (a) that the ostro- 

 coderms, especially those of the order Antiarchi to which Bothriolepis 

 belongs, are primitive vertebrates, and (b) that the Merostomata were 

 sufficiently generalized or plastic to have given origin to a group 

 radically different from that to which they belong. The theory re- 

 quires the origin of one highly specialized group of one phylum from an 

 equally highly specialized group of another phylum. It is much more 

 likely that the superficial resemblances of the two groups are both 

 adaptations for bottom-feeding, and that the heavily armored condi- 

 tion is evidence in both groups of senility. In general, groups of 

 animals are thought of as becoming armored as the result of 

 racial old age and a slowing down of the developmental vigor of the 

 constituent protoplasmic materials. The plastic young races retain 

 their flexibility and are as a rule without heavy integumentary de- 

 posits. From this point of view the ostracoderms fit very poorly into 

 the role of primitive or ancestral vertebrates. If the ostracoderms 

 cannot be used as the link between the fishes and the Merostomata, 

 the whole fabric of vetebrate phylogeny, as erected by Patten, breaks 

 up and falls apart. There is no question, however, as to the value of 

 Patten 's careful and exhaustive studies of comparative anatomy and 

 embryology of vertebrates and arachnoids, and especially valuable is 

 his contribution to our knowledge of the anatomy of the ostracoderms, 

 a group hitherto all too imperfectly known. The chief fault that one 

 finds with Patten's method of argument and exposition concerns his 

 skillful illustrations, which contain an ingenious intermingling of 

 fact and interpretation that is insidiously convincing unless one be 

 on his guard. Figures 42, 43, and 44 are among the most character- 

 istic of Patten's illustrations; and they speak for themselves. 



MINOR THEORIES OF VERTEBRATE ANCESTRY 



There are several other invertebrate groups that might conceivably 

 have given rise to the vertebrates. One of these is the vermian group 

 Nemertea, a group of uncertain affinities but related to the flat worms. 

 The Nemertean Theory of the Origin of the Vertebrates has been advo- 

 cated by Hubrecht, and the argument is based largely on the nervous 



