1899] ROCK-ANALYSIS 445 



rocks in which their presence would hardly have been suspected, and which in 

 ordinary analyses would have been unsought and overlooked. The translation 

 contains some additional remarks upon and references to the later observations 

 of Dr. Hillebrand, and on p. 33, a woodcut, not given in the original Bulletin, 

 illustrates the construction of a modified form of Gooch's apparatus, as employed 

 in the U.S. Survey laboratory for the determination of combined water. The 

 translation is well printed and has an index, but although it is a most useful 

 and convenient publication, the original Bulletin No. 148, with its well-tabulated 

 analyses, will probably be more frequently consulted in this country than 

 Dr. Zschimmer's careful translation. 



MESOZOA AND SPONGES. 



Traite de Zoologie Concrete. Lecons professees a la Sorbonne. Tome ii. 

 l re Partie Mesozoaires, Spongiaires. By Yves Delage and P^dgard 

 Hero hard. Pp. ix. + 244, with 15 coloured pis. and 274 figures in the 

 text. Paris: Librairie C. Reinwald, Schleicher Freres, 1899. Price 

 12s. Gd. 



The new instalment of this great work sustains the high level of its pre- 

 decessors in its fulness and clearness of exposition, and in its liberality of 

 excellent illustrations. The first part contains the fullest connected account as 

 yet published by the so-called Mesozoa, and is therefore of great interest. Four 

 classes are recognised: — (1) Mesocoelia, viz. Salinelia ; (2) Mesenchymia, in- 

 cluding Treptoplax and Trichoplasc ; (3) Mesogonia, comprising Dicyemiae and 

 Orthonectiae ; and (4) Mesogastria, viz. Pemmatodiscus. An appendix treats 

 of Physemaria, Cementaria, Pompholyxia, Kunstleria, and Siedleckia. The 

 authors have conferred a great boon on zoology, in bringing together the avail- 

 able information in regard to these obscure creatures which are as interesting 

 as they are puzzling. 



The second part deals with the sponges, to our knowledge of which Prof. 

 Delage has made some notable contributions. As was expected, there is a care- 

 ful discussion of the affinities of the class, in which Delage's own views are 

 naturally followed, though the diversity of opinion is duly recognised. The 

 classification adopted is as follows : — I. Calcaria, including Homocoelida and 

 Heterocoelida ; II. Incalcaria, including Triaxonia (Hexactinellida and Hexa- 

 ceratida) and Demospongiae (Tetractinellida, Monaxonida, and Monoceratida). 

 An appendix deals with the doubtful Abyssospongea, which probably do not 

 deserve the name. A zoological treatise on different lines may well be con- 

 ceived, but it will be hard to excel this one in clearness and fulness, or in beauty 

 of illustration. 



ELEMENTS OF VERTEBRATE EMBRYOLOGY. 



Die Elemente der Entwickelungslehre des Menschen unci der Wirbelthiere. 

 Anleitung unci Eepetitorium fur Stuclierende unci Aerzte. By Dr. 

 Oscar Hertwig, Director of the Anatomical-Biological Institute of the 

 University of Berlin. 8vo, pp. vi. + 406, with 332 figs. Jena : 

 Gustav Fischer, 1899 [dated 1900]. Price 7.50 marks, 8.50 bound. 



In twelve years Prof. Hertwig's well-known Lehrbuch has passed through 

 six editions, and has been translated into English, French, Italian, and Russian ; 

 and no one who has used it, whether as student or teacher, will wonder at its 

 great success. It is a model of lucidity, it is well illustrated, it is flavoured 

 with the salt of general ideas, and it is full of suggestion. 



But as he worked at the later editions, Prof. Hertwig began to feel that it 

 was impossible to cater for two sets of appetite. The expert wished for more 



30 NAT. SC. VOL. XV. NO. 94. 



