I 2 



SCIENCE. 



wilh the instrument can be reduced to within i per cent, 

 of the amount to be measured. It will register a 

 change in the temperature of the strips just described, 

 not exceeding 1-50,000 part of a Fahrenheit degree. 

 When mounted in a reflecting telescope it will record 

 the heat from the body of a man or other animal in an 

 adjoining field, and can do so at great distances. It 

 will do this equally well in the night, and may be said, 

 in a certain sense, to give the power of seeing in the 

 dark. A more valuable proof of its efficiency is shown 

 in a series of measurements of trie heat of the moon, 

 made under varied circumstances, to guard against error, 

 but each made in a few seconds. All these measure- 

 ments show that the almost immeasurably minute am- 

 ount of heat from the moon can be certainly measured by 

 it, even with a common refracting telescope. 



CORRESPONDENCE. 



[ The Editor docs not hold himself responsible for opinions expressed 

 l<y his correspondents. No notice is taken of anonymous communi- 

 cations.] 



To the Editor of Science :— 



In a recent issue of " SCIENCE," " B. G. W." in a very 

 instructive review of Marsh's monograph on the limbs 

 of the Sauranodon, speaks of Darwin's hypothesis re- 

 garding sexdigitism in man, as reluctantly abandoned 

 by that evolutionist, but as now standing some chances 

 of rehabilitation owing to the discovery of sexdigitism 

 as a normal feature of the extinct genus Sauranodon. 

 Probably the reviewer has not met with a treatise, in 

 in which a certain discovery of an embryonic peculiarity 

 is detailed, and which explains not only the occurrence 

 of sexdigitism but of polydactylism in man. As this 

 treatise is in the hands of few comparative anatomists, I 

 may refer to the facts here at some length. In figure 76 

 on page 137 of Schenk's Lehrbuch der vcrgl. Embryo- 

 logie der Wirbelthiere (Vienna, 1874), is represented a 

 section taken flatwise through the embryonic human 

 paw. The chondrogenic elements of the mesoblast can 

 be seen arranged in strands, indicating the metacarpo- 

 phalangeal rays. A sixth ray seems very clearly present, 

 and from some of the other rays lateral processes spring, 

 which in the course of normal development become 

 merged into the main ray, no doubt. 



On this head, as well'as some others related to the 

 temporary presence of ancestral features in the exremi- 

 ties of the human embryo, I have written as follows in 

 a series of lessons on embryology, published in the St. 

 Louis Clinical Record : 



At the points where the head and tail were respectively 

 deflected from the trunk the peripheral protovertebrol 

 masses are buiged out, as it were, and thus we have twa 

 anterior and two posterior ill-marked eminences com- 

 posed of mesoblast elements covered by the cutaneous 

 epiblast. These are the anterior and posterior extremi- 

 ties. The posterior pair is the earliest to be discovered, 

 but it is so rapidly outstripped in growth and develop- 

 ment by the anterior extremities, that the belief has be- 

 come current that the anterior are the first to appear, 

 which is incorrect. 



At the time when the hand has become demarcated 

 from the forearm by the wrist constriction, the forearm 

 has not yet become separated from the arm. And in 

 like manner the foot is individualized before the leg and 

 thigh are demarcated. The fingers are developed before 

 the toes, and in both the hand and foot the digital seg- 



mentation is preceded by a stage in which there is a fold 

 formed separating a main mass from the aggregate 

 digital mass, and which persists in the adult. 



If a surface section be made of an embryonic hand or 

 foot before the digits are formed, we will find that the 

 cell-strands which constitute the basis for each meta- 

 carpophalangeal ray are not five, as in the adult and 

 developed foetus, but are from seven to nine (at different 

 periods) in number. This remarkable fact, discovered 

 by my teacher, Prof. Schenk, of Vienna, points, in a man- 

 ner, to the descent of the pentadactylous animals, to 

 which man belongs, from the enaliosaurians or analogous 

 groups of thejurassic and triassic periods of the earth's 

 history whose fossilized remnants clearly show that they 

 had seven or more fin rays. 



To many, another and related fact will prove still more 

 convincing in an evolutional point of view, although 

 Schenk's observation is of more fundamental importance 

 than the following to zootomists : 



Hensen, of Kiel, discovered that, in a human embryo 

 of the seventh week, the fingers and toes are provided 

 with claw-like appendages like the claws of camivora, 

 and that these structures are exfoliated to make way for 

 the true nails. Further, he found plantar and palmar 

 eminences like the foot-pads of the dog, cat and mar- 

 supial carnivores* E. C. Spitzka. 



New York Jan. 7, 188 r. 



BOOKS RECEIVED. 

 Was Man Created ? By Henry A. Mott, Jr., Ph. 

 D. Griswold and Company, New York. 



The time is still distant when conclusions will be 

 drawn on the subject of the Origin of Man and many 

 ether problems treated by the author of this book. 

 Material is accumulating faster than it can be arranged, 

 but in all probability, a thousand years hence we shall 

 still be without sufficient data and be diligently searching 

 for evidence. 



The scientific man is not discouraged on this account, 

 but is well content to work on, adding daily to the great 

 store-house of knowledge, indifferent as to whether 

 final results are arrived at in his own day or in the 

 future. 



There is, however, another class of persons in society, 

 who, finding .that certain scientific truths, which are 

 undeniable, conflict with revealed religion, desire a more 

 speedy solution of these questions. 



Dr. Mott in his book attempts to outline a middle 

 course for those who are forced by scientific discovery to 

 renounce the Biblical teachings respecting the Origin of 

 Man, by showing from a large number of authorities, 

 that a belief in the dual existence of man may be held 

 upon reasonable testimony. 



Had Dr. Molt called his book " An Introduction to 

 the Study of the Origin of Man and his Future Destiny," 

 we think it would have been an appropriate title, and 

 would have commanded a large class of readers who are 

 unable to obtain the larger works consulted by the au- 

 thor ; and the seventy-five illustrations, which are well 

 selected, would have been of considerable service to such 

 persons in grasping the subject which is naturally com- 

 plicated to those who approach it for the first time. 



Dr. Irvine, of Glasgow, recently exhibited and ex- 

 plained before the Mining Institute of Scotland, his new 

 safety-lamp, which is constructed to emit a loud sound 

 when an explosive mixture of gas and air enters it, and 

 thus consequently indicates fire damp in colleries. 



* Development of the Human Ovum Embryo, and Foetus, St. Louit 

 Clinical Record, (Lecture VIII.) June, 1880. 



