NATURE 



361 



THURSDAY, FEBRUARY 20, 1896. 



EMBRYOLOGY. 

 Text-book of the Embryology of Invertebrates. By Dr. 

 E. Korschelt and Dr. K. H eider. Part I. Translated 

 from the German by Edward L. Mark and W. McM. 

 Woodworth. Pp. xvi + 484. (London : Swan Sonnen- 

 schein and Co., 1895.) 



EMBRYOLOGY "is one of the most important 

 subjects in the whole round of Natural History." 

 So says Darwin, and so say all zoologists who have the 

 knowledge to appreciate, and the training and patience 

 to deal with, the innumerable facts which constitute 

 that most fascinating branch of their subject. 



Formerly the view was held— it is even now held by 

 some zoologists — that embryology is a subject apart 

 from the other branches of zoology ; that a man might 

 be a complete zoologist without any knowledge of it ; 

 that it could throw but little light upon those great 

 ■questions of structure which it is the ambition of com- 

 parative anatomy to solve ; and that it was a study which, 

 if it did not actually narrow the mind, took it away from 

 that pure and sympathetic contemplation of nature, 

 which it was the object of all true zoological teaching to 

 call forth. To such zoologists embryology was of but 

 small importance. 



And the reason for this attitude is not far to seek. In 

 the good old days the equipment required by the 

 zoologist was but slight, and the facts lay bare for every 

 one to note. A collecting-box and a bottle of spirits, a 

 pocket-lens and, by the more advanced, a pair of forceps 

 and a scalpel were all that were required. With such 

 simple instruments, combined with a certain power of 

 observation and a love for nature, which had often more 

 of an aesthetic than a scientific character, a man might 

 go far. But this delightful time is past — the unaided 

 pocket-lens is now of little service, the forceps and 

 scalpel have revealed almost all that they are capable of 

 revealing, and the bottle of spirits requires to be 

 supplemented by a whole complement of elaborate 

 reagents. And if this is true of the material requisites, 

 how much more true is it of the intellectual. In addition 

 to the elaborate technique, the complicated instruments 

 and the whole routine of the modern laboratory, there 

 are the immense accumulations of knowledge which 

 must be mastered if nature is to be questioned with any 

 hope of success. It is this training which is often irk- 

 some ; it is these instruments which cannot be used 

 without patience and practice ; which bewildered the 

 older zoologists, and which make the way so hard for 

 those younger men who, with a collector's or an assthetic's 

 love for nature, wish to pose before the world, after the 

 manner of their fathers, as experts in an important 

 branch of science. 



But to return to our question : What is the relation of 

 embryology to the other branches of zoology ? Clearly 

 it is an integral part of the well-known and respected 

 science of comparative anatomy ; it is the part of that 

 science which deals with the anatomy of the organism 

 before the attainment of sexual maturity, and, inasmuch 

 as most animals pass through several stages of structure 

 NO. 1373. VOL. 53I 



during their growth, the study of it is, to the scientific 

 anatomist at least, as important as the study of the adult. 

 One would have thought that this position would have 

 been conceded on all hands, and that there would have 

 been no necessity to call attention to it here. But it is 

 not so ; for there are anatomists who hold that, in solving 

 anatomical problems, the structure of the embryo is of 

 very small importance indeed as compared with the 

 structure of the adult. 



But embryology is more than this. It has caused the 

 use of methods and instruments which have extended 

 the bounds of comparative anatomy ; it has brought into 

 the field men who, in their love of nature, in their capacity 

 for patient labour, and in their powers of accurate ob- 

 servation, are at least the equals of the older naturalists ; 

 and it has brought to light facts of natural history which, 

 but for it, would have remained in darkness, and which 

 even that zoological butterfly, the amateur naturalist, 

 would not pass by. To mention only a few such. What 

 more wonderful phenomena can be mentioned in the 

 whole round of natural history than the larval develop- 

 ment and metamorphosis of the Echinoderinata ; the 

 detachment and digestion of the brain and sense organs 

 of the larva of Phoronis on the attainment of sessile life ; 

 the growth of the worm within the larval skin of the 

 Pilidium ; the double sexual life of the Ctenophora. 



Of the relation of embryology to the evolution theory, 

 we can only shortly refer. Apart from the construction 

 of phylogenetic histories, to which unfortunately there 

 appears to be no end, our science is of supreme im- 

 portance as affording the most unanswerable, indirect 

 corroboration of that theory which it is possible to obtain. 



But embryology has wider bearings even than these. 

 The systematist is powerless without it. He may ignore 

 it, he may neglect it ; but if he do so, he can have no true 

 insight into the relations of the great groups. Until 

 embryology was a science, the Tunicata were grouped 

 near the Mollusca ; and without its aid the great Cuvier 

 himself was led into the error of placing the Cirrepedia 

 in the same phylum. Nor can the student of species 

 avoid his fate. To-day he may rejoice that he at least 

 can pass by on the other side, and leave embryology to 

 the embryologists. But, alas ! it will not be so for long ; 

 even now embryonic characters are beginning to assert 

 their claims for recognition, and in the near future a 

 knowledge of development will be as indispensable to 

 the species-monger as to any other kind of zoologist. 



It would thus appear that embryology has a classifi- 

 catory as well as an anatomical value, and should be 

 dealt with in works on zoology. But while in works on 

 anatomy it is quite impossible to ignore the facts of 

 development, it is unfortunately true that in zoological 

 treatises, systematic embryology is either entirely neg- 

 lected or else treated in such a sketchy way as to be 

 useless, or nearly so, to the student. But in saying this, 

 we desire to impute no blame to zoological authors, who 

 are already overburdened with the immense mass of 

 facts which they have to treat. Hence the necessity for 

 books specially dealing with the subject — books which 

 had their model and initiator in the great work on 

 comparative embryology by F. M. Balfour, The book 

 before us may, indeed, almost be regarded as a second 

 edition of that work, so closely are Balfour's plan and 



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