1897.] A Chapter in the History of Science. 847 
evsky published a memoir sustaining the thesis that the Tun- 
icates were members of the vertebrate phylum, and that the 
larval stage of most of the species had the homological equiv- 
alent of the backbone of the true vertebrates. Cope foresaw 
the morphological consequences of this view and sought the 
vertebrates nearest the Tunicates. He settled upon some 
strange forms of the Silurian and Devonian times known as 
Pteraspids and Cephalaspids. They were the earliest known 
of vertebrates and, therefore, likely to be the most primitive 
in structure. Most of them had a shell-like encasement, com- 
posed of bone-like plates. He happened to find illustrations 
of the living Chelyosoma, a true Tunicate, having a system of 
plate-like indurations of the integument, somewhat similar in 
appearance to those of some of the ancient fishes. It was as- 
sumed that this mere superficial similarity indicated genetic 
relationship. To those acquainted with the structure of 
Chelyosoma this approximation seemed strange indeed ; its 
anatomy was known and the form is simply a well marked 
relation of the typical Ascidiids, but highly specialized by the 
development of integumentary plate-like horny indurations. 
Histologically and otherwise they were very different from the 
plates of the extinct armored vertebrates. Cope’s guess was 
simply the result of the tendency to jump at conclusions which 
he was constantly obliged to curb, and unfortunately he 
rushed into print before he had timetothink. He soon recon- 
sidered the case with calmer mind, and abandoned his hypo- 
thesis. Few men were ever more willing to reconsider evi- 
dence and retrace false steps than was he. 
In spite of errors of detail and somewhat hasty generaliza- 
tion the ichthyological labors of Cope were unusually valuable 
contributions to science, and the progress of ichthyology has 
‘been much accelerated, not only by these labors, but by the 
investigations they challenged. 
V. 
Cope’s attention was early drawn to the mammals. His 
first published article (1863) was a description of a supposed 
new Shrew found in New Hampshire, and in 1865 he described 
58 
