Feb., 1895. SOME NEW BOOKS. 127 



wrongly to the excretory system of Trematodes and Turbellaria, and 

 that it is phylogenetically of the same order as that of the Nemertines 

 and the flat-worms, thus confirming the opinion of Whitman upon 

 this point. 



One of his main arguments for this view is drawn from the pre- 

 sence of cilia within the tubes. We have, as he points out, no reason 

 for supposing that cilia, which are characteristic structures of the 

 outside of cells, ever grow upon the inner sides of the cell-wall. 



At the end of the anatomical part of the paper some interesting 

 biological notes are given. Most of the ectoparasitic Trematodes live 

 attached to the gills of fishes ; but some live in the mouth-cavity or 

 on the general surface of the body. When two species are found 

 living on the same fish, generally they confine themselves to separate 

 regions. Thus Tvistomum sinuatum and T. ovale live upon a Histiophovus, 

 but the latter confine themselves to the mouth-cavity, the former to 

 the inner surface of the branchial plates. 



When removed from the host and placed in water many of the 

 Trematodes move about by looping movement, using their suckers like 

 those of the leech. Most of them live upon the slime of their host, 

 but a few are able to extract blood. 



Most of the monogenetic Trematodes have a colourless and trans- 

 parent body in which the vitellarium and the pigment cells of the 

 intestine are the only coloured parts. However, says Mr. Goto, 

 " This must not be regarded as a case of protective colouration ; for, 

 in the first place, the nature of the habitat already protects the 

 parasites from being attacked by their enemies, and in the second 

 place, they are but very imperfectly exposed to light and thus the 

 conditions of their existence prevent any effective play of Natural 

 Selection." 



A History of the World. 



Die Vorwelt und ihre Entwickelungsgeschichte. Von Dr. Ernst Koken, 

 Professor an der Universitat Konigsberg. 8vo. Pp. viii., 655, with two folding 

 maps and 117 text figures. Leipzig: T. O. Weigel Nachfolger. 1S93. 

 Price 14s. 



The change that has taken place in the position of geology since the 

 early years of this century nowhere makes itself more felt than in a 

 book such as the present. In former days a Humboldt or a Lyell 

 could appeal with safety to a larger public : vistas were then being 

 opened that stirred the imagination of all ; the broad lines of the 

 drama arrested the attention ; and details gave no trouble, because 

 details were still unknown. Nowadays we know so much, and we 

 have pushed out into the darkness in so many directions, that a 

 comprehensive survey is a task of far greater difficulty : we are 

 overwhelmed by the extent and by the specialisation of our informa- 

 tion ; it is the details that interrupt our vision, and " we cannot see 

 the wood for the trees." In these respects, too, the geologist, whose 

 science is a compound of so many other highly-specialised sciences, 

 of physics, of chemistry, of zoology, and the like, — the geologist or the 

 historian of the whole earth stands at a great disadvantage as com- 

 pared with the historian of but a small portion, or of a small and 

 unremote period. The archaeologist and the man in the street soon 

 find a common platform and a common speech, but the geologist of 

 to-day no longer tells his story in the vulgar tongue. These difficulties 

 have been fully understood by Dr. Koken, and his book, written for 

 the most part in a flowing and distinguished German, is an excellent 

 attempt to overcome them. He will not, however, spare his readers 



