June i, 1905] 



NA TURE 



is in millimetres. The rules can be supplied with the 

 plain scales either in inches or millimetres, and in the 

 specimen submitted to you the mix up is the result of 

 accident, and not perversity. , 



John- Davis and Son. 

 All Saints' Works, Derby, May 20. 



THE LO,WER VERTEBRATES.' 



EVERYTHING comes to him who waits V ! 

 Certain!}- the patience of n^any has been sorely 

 tried by the long- advent wliicli has preceded the 

 appearance of this last volume of the Cambridge 

 Natural History. Students of the lower vertebrates 

 will be naturally predisposed,:. to accord it a favourable 

 reception, inasmuch as its predecessors have presented 

 such a high standard Cif excellence^ If in some 

 respects a closer acquaintance reveals some cause for 

 complaint it will be admitted that, surveyed as a 

 whole, both autliors and e(3itors ahke are to be con- 

 gratulated on having produced a work of sterling 

 merit. ,,, , 



The groups dealt with' in this volume are not only 

 of the highest scieQtjfi^ interest and importance, but 

 they present more than ordinary difficulties to be 

 investigated, and these difficulties are materially 

 increased when stern necessity compels the several 

 contributors to condense tlieir work within the smallest 

 possible limits. Happily this task has fallen on the 

 right shoulders, and all must admire the way in which 

 it has been performed. 



The first chapter of this book has been written by 

 Dr. S. F. Harmer, and deals with the Hemichordata, 

 a group which includes creatures of the existence of 

 which the layman has never heard ! Yet their import- 

 ance in the scheme of evolution is of the highest, in- 

 asmuch as they bridge the gap for us between verte- 

 brates and invertebrates. 



The true nature of these worm-like and tubicolous 

 animals has been determined only after the most 

 laborious and painstaking research, in which Dr. 

 Harmer, the author of this chapter has borne a very 

 conspicuous share. Though the vertebrate affinities 

 of the worm-like Balanoglossus were first hinted at 

 by Kowalewsky in i<S66, it was not until 1886 that 

 this relationship was really demonstrated ; a triumph 

 achieved by Bateson. Forming at first a branch by 

 Itself of the vertebrate phylum, Balanoglossus has 

 iince lost something of its unique character by the 

 discovery that certain other tubicolous forms — 

 Rhabdopleura and Cephalodiscus — would have to be 

 promoted to share this position, though to the ordinary 

 observer nothing could be less like a vertebrate in 

 appearance ! This advance in our knowledge was 

 made by the author of this chapter ; and he has now 

 still further extended the boundaries of this group so 

 as to include Phoronis, an animal hitherto referred 

 both to the Gephyrea and to the Polyzoa. 



Although our knowledge of the Tunicates — those 

 " common objects of the sea-shore," known as the 

 " sea-squirts " — has been accumulating for some- 

 thing more than two thousand years, it was not until 

 the middle of the eighteenth century that any real 

 progress in the study of these creatures was made. 

 And yet a century passed before the appearance of 

 Kowalewsky's epoch-making work, which showed con- 

 clusively the astonishing fact that these shapeless 

 jelly-bags were really kith and kin of the vertebrates — 

 but degenerates ! 



No other group of animals is so all-embracing in 

 the nature of the phenomena it displays. As the 

 author remarks, " They demonstrate both stable and 



'"Hemichordata, Ascidians and Amphioxus, Fishes." By Drs. 

 Harmer, Herdman, Bridge and G. S. Boulenger. The Cambridge Natural 

 History, vol. vii. Pp. xvii + 760. (London; Macmillan and Co., Ltd., 

 1904.) Price 17J net. 



variable species, monophyletic and polyphyletic 

 groups. They exhibit the phenomena of geinmation 

 .ind of embryonic fission, of polymorphism, hiberna- 

 tion, alternation of generations, and change of func- 

 tion. They have long been known as a stock example 

 of degeneration ; but in fact they lend themselves 

 admirably to the exposition of more than one ' chapter 

 of Darwinism.' " 



Prof. Herdman has made this group peculiarly his 

 own, and the editors are to be congratulated in 

 having secured him to write this chapter. Nowhere 

 else will the student find so complete and altogether 

 admirable a summary of this most difficult and 

 puzzling group of animals. 



In dealing with amphioxus Prof. Herdman has 

 been hampered by lack of space. Tliis seems evident, 

 not from, the absence of any essential facts in his 

 account, but from the condensed fashion in which the 

 facts are presented. To the majority of those who 

 will use this book this is perhaps of no great moment, 

 but others, we imagine, will fail to appreciate the full 



Fig. I. — Embryos of Kkodeus «.. 

 e. Embryos ; gt inter-lamellar 

 Natural History." 



in the gili-cavities of Unic. 

 ities. From the " Cambridge 



NO. 1857, VOL. 72] 



importance of some phases in the life history of this 

 "weed in the vertebrate garden." 



The remarkable ciliated condition of the embryonic 

 and early larval stages is, for example, all too lightly 

 passed over. Attention is not called to the importance 

 of the fact that in the free-swimming, ciliated larva we 

 have a connecting link between vertebrates and in- 

 vertebrates. His reference to the existence of cilia 

 is of the briefest. He remarks simply, that " the 

 embryonic stages being passed through during the 

 night ... the larva hatched in the early morning," 

 and then, on the next page, continues, " The epiblast 

 cells become ciliated all over the surface, so that the 

 embryo rotates within the thin covering which still 

 surrounds it." Passing on to describe the meta- 

 morphosis of the embryo he goes on to say that " When 

 it has (developed) about five pairs of niesoblastic 

 somites, it breaks out of its covering, and becomes_ a 

 free sv.'imming larva." Probably no living biologist 

 knows more of amphioxus than Prof. Herdman. 

 Thus, then, this lack of emphasis of a really important 

 feature must be attributed to the fact that he had to 



