420 THE POPULAR SCIENCE MONTHLY 



Most of the theories were mutually exclusive; none of them were based 

 on detailed comparisons of several systems of organs ; and none of them 

 threw any light on vertebrate anatomy, or afforded even an approxi- 

 mate solution of the real problem. 



The vital spark in these theories vanished long ago, but certain basic 

 postulates in them have slowly petrified into the semblance of estab- 

 lished facts and have introduced into morphology many false ideas, and 

 a system of nomenclature that implies a knowledge we by no means 

 possess. Many a zoologist, proud of his adherence to sound zoological 

 principles, accepts these familiar terms as evidence that the things so 

 named are really what the names imply, as, for example, the terms 

 dorsal and ventral, right and left, gastrula, archenteron, blastopore 

 and ccelomic pouches. The same subtle transformation of theory into 

 fact is shown by the perpetuation of the view that the notochord is 

 made of endoderin because it arises from the walls of the " archen- 

 teron " ; and by the one that the primitive streak represents the closed 

 lips of an " Uhrmund." 



When real progress along the old lines ceased, the problem came to 

 be regarded as hopeless, largely because it was assumed that the ances- 

 tors of the vertebrates were small, soft-bodied animals, unlikely to be 

 preserved as fossils. The " practical " biologist then turned his atten- 

 tion to cytology, experimental evolution and genetics, and the study of 

 morphology and phylogeny became almost as discreditable an occupa- 

 tion, especially in the eyes of the new school of biologists in this 

 country, as the study of metaphysics, or the description of new species. 



During this long search for the ancestors of the vertebrates, the 

 arthropods (insects, Crustacea and arachnids), the largest and most 

 highly organized class of invertebrates were altogether excluded, with 

 astonishingly aggressive unanimity, from their due consideration. It 

 is difficult to understand this impenetrable state of mind, for it did 

 not appear to be based on any known facts, or upon any positive evi- 

 dence whatever. It was apparently due to a widespread conviction 

 that the general trend of evolution in the arthropods did not lead toward 

 the vertebrates, that the arthropods themselves were too highly special- 

 ized to give rise to a new type, and to the fact that the hue and cry of 

 the annelid theory was leading the chase in another direction. 



In view of this situation, it may be readily understood that another 

 attempt to connect the genealogy of the vertebrate stock with that of 

 the invertebrates will now have to contend with a widespread indiffer- 

 ence born of repeated failures; with interests already diverted into 

 other channels; and with that first, unreasoning hostility that is the 

 protective attitude of the mind toward any strange idea that threatens 

 to steal away our cherished convictions. « 



