APPENDIX 



THE GENERAL METHODS OF EMBRYOLOGICAL RESEARCH 



Embryology is one of the youngest of the sciences and it offers a wide field 

 for fascinating and important research. Regarded as a branch of morpho- 

 logy its main object is to gain information concerning the lines along which 

 the structure of existing groups of animals has evolved. In the phylum 

 Vertebrata there is an immense amount of work still to be done and it is 

 important that the would-be researcher should be guided by certain, general 

 principles as to the technique of the subject, otherwise he is apt to achieve 

 no more than the addition of relatively unimportant details to the vast 

 accumulation of details which during the past few decades has tended to 

 hide away general principles and incidentally to smother interest in the 

 subject. 



The incompetent or inexperienced investigator frequently betrays him- 

 self by his choice of subject : he chooses a problem of relatively minor 

 interest when there lie ready at his hand others which are of real importance, 

 or he chooses a subject really important but -of such difficulty that the 

 probabilities are heavily against the feasibility of its solution under 

 existing conditions. The beginner then should see that he has the aid of 

 some competent adviser before he decides upon his line of research. 



Having chosen his particular problem he has next to decide regarding 

 the particular animals upon which his research is to be carried out. The 

 earlier workers were guided mainly by the accessibility of the material. 

 Fowls and Rabbits — ■ of which embryos were easily obtained and easily 

 investigated — provided the material for the great pioneers of vertebrate 

 embryology and the embryology of to-day suffers much from the difficulty 

 of getting rid of general ideas founded on such narrow bases. Now that 

 embryology has taken its place as a branch of evolutionary science we 

 recognize the importance of basing our general ideas upon the phenomena 

 of development as displayed by the more primitive existing groups. In 

 attempting any important problem of vertebrate morphology evidence 

 must be got from Elasmobranchs, Crossopterygians, Lung-fishes, Urodeles, 

 before we can feel completely confident as to general principles : in other 

 words we must go to groups which are admittedly archaic. Apart from 

 directly adaptive features an animal which is archaic in its adult structure 

 may be expected to show primitive features in its development. Naturally 

 we should not look for this in cases where development takes place under 

 peculiar conditions, for these necessarily involve adaptive modification. A 

 pitfall into which investigators frequently stumble is that, starting from 



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