66 Miss Agnes Crane — Evolution of the Brachiopoda. 



Darwin. Formerly regarded as one of the most obstinate difficulties 

 in the way of the demonstration of the evolution of invertebrate life 

 on earth, they now bid fair to become a remarkable illustration in 

 favour of it. It is no longer possible to doubt that the life-histoiy 

 of the Brachiopoda does yield convincing testimony of the truth of 

 the law of Evolution, and to the establishment of this fact American 

 scientists have largely contributed. Their work is the more creditable 

 to them because so often carried on amidst a constant fight for 

 " appropriations " and a liability to upset from the exigencies of the 

 political situation — trials happily unknown to our more favoured, 

 scientists. In the Western world the minds of scientific workers in 

 general seemed more favourable to the acceptance of the great 

 principles of Evolution conceived and first promulgated in Europe. 

 In America they sought rather to prove the argument than to con- 

 trovert it. They were, perhaps, less blinded by that third, eyelid 

 " the nictitating membrane " which their genial and witty philosopher, 

 Wendell Holmes, has declared to be common alike "to reptiles, some 

 birds, and theological students," and by means of which, he said, 

 " they shut out," not all the light, " but all the light they do not 

 want I" The genus is not absolutely unknown in this country, 

 although more rare than formerly. It is to American biologists that 

 we owe not only the systematic correlation among invertebrates of 

 the development of the individual (ontogeny) with the phylogeny 

 or evolution of the group to which it belongs, but also the important 

 discovery of the radicals of many classes of molluscan animals. 

 Such ancestral root-stocks have been determined by Hyatt for the 

 Cephalopoda, by Jackson for Pelecypoda (in Nucula), and by 

 Beecher for the Brachiopoda. The radical of the Bracliiopoda is the 

 Lower Cambrian genus the father-like Paterina, of which more anon. 



The Brachiopoda, it is well known, have persisted through all 

 the life epochs of the geological past. Their bivalve shells occur 

 fossil in all marine deposits ranging from the Primordial to the 

 Quaternary. They were, however, much more abundant during 

 the " old time " and medial ages of geological history than during 

 these "latter days" of the earth. Out of the 277 described genera 

 186, or two-thirds of the whole number, appeared in Pal830zoic seas, 

 and a goodly number were evolved during the great Secondary epoch. 



Thousands of species or " mutations " have existed in the past, 

 but now they can be numbered by tens instead of by thousands, 

 for there are fewer surviving species than there were genera in the 

 Palseozoic era. The actual number of living species was estimated 

 by Davidson— in that posthumous " Monograph on the Recent 

 Brachiopoda " which it became my sad duty to edit for the Transac- 

 tions of the Linneean Society — at 99 certain, and 29 doubtful species, 

 referable to 22 genera and subgenera. With the modern tendency 

 to generic subdivision and sti'icter revision of species it is probable 

 that this estimate will be reduced rather than augmented, so far as 

 the number of species is concerned (27).^ 



1 These numbers, in parentheses, refer to the Bibliography given at the end of 

 Part II.— Edit. G.M. 



