IS94. SOME NEW BOOKS. 459 



which the structure of this animal gives rise to are included. Mr. 

 Willey quotes no less than 133 papers which have been consulted by 

 him in the course of preparing the volume now before us, and of these 

 at least 100 may be fairly put down to Amphioxiis itself. It is there- 

 fore a saving of much time to the hard-worked zoologist of the present 

 day to have all this in a nut-shell — a cocoa-nut-shell possibly, — but 

 still a work of moderate dimensions. Apart from this merit, the 

 practice of writing a book about a definite animal of interest seems to 

 us to be an excellent plan. It is a pity that not more is done along 

 this hne, which was really initiated by Mr. Huxley in his " Crayfish." 

 The anatomy of birds, for example, might be woven into a volume 

 upon such a type as Aptcvyx, one upon the Amphibia upon a plain 

 account of the Axolotl, and so forth. 



The present work contains everything that should be known 



about Amphioxiis, besides a great deal that it is advantageous to know 



about the Tunicata, Balanoglossiis, and some other types which come 



into structural relations with Amphioxiis. Amphioxiis was originally 



put down as a Mollusc, a fate which also overtook another equally 



remarkable and not less isolated type, Pevipatus ; the Mollusca in the 



early days of this century and the last days of the seventeenth 



appear to have been pretty well what the worms are now, a receptacle 



for anything unclaimed. The Russian naturalist Pallas, the discoverer 



of the " fish," was responsible for this placing of it; it was not until 



sixty years had elapsed that Costa redescribed Amphioxiis and 



put it in its proper place, approximately at any rate. Nowadays 



there are really two parties which surge round Amphioxiis ; there 



are those who would look upon it as much degenerate and those who 



regard its simplicity as a mark of antiquity. There is no doubt much 



of both in the organisation of the animal. This " exquisite form," as 



Professor Osborn enthusiastically calls it in the preface which he 



contributes to Mr. Willey's book, is common in many parts of the 



world ; it is, indeed, practically world-wide in range, or is represented 



by a considerable number of species which differ in but slight 



characters, the number of the myotomes being the chief means by 



which they are distinguished. Mr. Willey argues from its wide range 



and the trifling specific differences that the form is extremely ancient. 



We fully agree with Mr. Willey that the creature is in all probability 



an extremely archaic form, but his reasoning does not seem to us to 



prove the fact. In ancient forms it is surely more usual for the 



differences between species, or genera, as the case may be, to be great 



rather than small ; intermediate forms have had time to die out, and 



long isolation has done its work. It is, rather, the newer groups that 



fade imperceptibly into each other. The very fact that there are so 



many diverse opinions about the classification of birds is indirect 



evidence of the comparative newness of the group ; while the 



strikingly marked lines which divide from each other the several 



groups of reptiles are confirmatory of their age as shown by the rocks. 



The number of described species of Amphioxiis is eight, but we 



believe that a ninth species was described at the recent meeting of 



the British Association at Oxford. 



Amphioxiis is, as will be inferred from what we have said concern- 

 ing the bulk of the literature devoted to it, one of those animals which 

 most naturalists have had dealings with. It is surprising, therefore, to 

 learn howrecently the excretory system has been discovered. For a long 

 time the animal was believed to be without any specialised excretory 

 organs of the vertebrate type — a piece of evidence which appeared to 



