LITERARY NOTICES. 



129 



and the peripheral portion the vascular wall, 

 and in birds the red cells arise from the walls 

 of the venous capillaries of the bony marrow. 

 In other words, the blood-cell is a liberated, 

 specialized endothelial cell. 



One of the most interesting and valuable 

 chapters in the volume is that on the germi- 

 nal area and the embryo and its appendages, 

 in which there is a synopsis of the published 

 descriptions of embryos not over three weeks 

 old ; from these it is learned that no human 

 ovum has been observed to have a primitive 

 streak, which is the first stage of the series 

 formulated by the author. In this stage 

 (twelfth or thirteenth day) the human ovum 

 is a rounded, somewhat flattened sac of three 

 or four millimetres in diameter, bearing an 

 equatorial zone of short, unbranched villi that 

 are probably formed by the ectoderm only ; 

 the wall of the sac is ectoderm, whether un- 

 derlaid by somatic mesoderm or not is uncer- 

 tain ; a mass of cells is attached to the inner 

 wall of the sac, over one of the bare poles of 

 the ovum, constituting the rudiment of the 

 embryo. The second stage is characterized 

 by the appearance of the medullary plate, the 

 third by the appearance of the medullary 

 groove, the fourth by the formation of the 

 heart and medullary canal, the fifth by the 

 development of the first external gill-cleft, 

 the sixth by the appearance of two external 

 gill-clefts, the seventh by the appearance of 

 three gill-clefts, and the eighth by the ap- 

 pearance of four external gill-clefts. 



The fourth part of the work includes de- 

 scriptions of the chorion, the amnion and 

 proamnion, the yolk-sac, allantois, and um- 

 bilical cord, and the placenta. 



The final portion of the volume is de- 

 voted to chapters on the growth and devel- 

 opment of the various organic systems of the 

 foetus. 



Each section and chapter aims to present 

 a comprehensive review of the literature re- 

 garding the subject therein considered, the 

 author stating the reasons for accepting cer- 

 tain theories in preference to others. One 

 blemish in the volume is the free use of Ger- 

 man embryological terms. The author's de- 

 votion to German has often led him to use, 

 also, forms of expression that, while correct 

 in German, are faulty English. This is, how- 

 ever, a minor and remediable fault in what 

 is a most excellent book. 



VOL. XXIII. — 10 



Pioneers of Science. By Oliver Lodge, 

 F. R. S. London : Macmillan & Co., 1893. 

 Pp. 404. Price, $2.50. 



This work consists of a course of eight- 

 een lectures on the history and progress 

 of astronomical research, with biographical 

 sketches of each pioneer and an examina- 

 tion of their influence on the progress of 

 thought. It is divided into two parts. The 

 first, which is entitled From Dusk to Day- 

 light, contains ten lectures giving a brief 

 outline of the physical science of the an- 

 cients, with an interesting account of the 

 progress of astronomy from Thales, 640 b. c, 

 to the death of Newton, 1727 a. d. The 

 second part is called A Couple of Centu- 

 ries' Progress, and embraces the period of 

 astronomical discovery from the publication 

 of Newton's Principia to the present time. 



The author shows considerable power of 

 lucid condensation in his description of the 

 labors of the early astronomical scientists, 

 and while giving a brief history of their 

 discoveries — notably those of Archimedes, 

 Ptolemy, and Roger Bacon — he brings us at 

 a bound over the void of the middle ages 

 to the beginning of the sixteenth century 

 (1543) when Copernicus (Nicolas Copernik) 

 published his famous work, De Revolutioni- 

 bus Orbium Coelestium, in which he proved 

 that the earth is a planet like the others, and 

 that it revolves round the sun — thus shatter- 

 ing the accepted Ptolemaic system and revo- 

 lutionizing all other (speculative and theo- 

 logical) doctrines concerning the form of the 

 earth and the motion of the heavenly bodies. 



This period is called by Mr. Lodge " the 

 real dawn of modern science." His sketch of 

 Tycho Brahe is most interestingly written ; 

 and in the summaries of facts which preface 

 each lecture will be found some curious coin- 

 cidences of the dates of the birth and death 

 of the famous philosophers from Copernicus 

 to Newton. While admitting the great labors 

 and immense value to astronomical research 

 of Galileo's discoveries, the author does not 

 class him with Copernicus, Kepler, or New- 

 ton ; in fact, he says that " Archimedes and 

 Galileo can only be considered in the light 

 of experimental philosophers." Lord Bacon, 

 who flourished about the same time as Des- 

 cartes, is very summarily dismissed ; he does 

 not admit him into his list of philosophers, 

 and says : " His (Bacon's) methods are not 



