SUMMARY OF CURRENT RESEARCHES 



RELATING TO 



ZOOLOGY AND BOTANY 



(principally invertebrata and cryptogamia), 



MICROSCOPY, Etc.* 



ZOOLOGY. 



VERTEBRATA. 

 a. Embryology, t 



Shapes of Eggs.} — D'Arcy W. Thompson discusses the factors which 

 determine the shapes of the eggs of birds. Eggs may be spherical, 

 elliptical, ovoid, or blunt at one end and pointed at the other. Selec- 

 tionist interpretations suggest that the pointed egg is less apt than a 

 spherical one to roll off a narrow ledge of rock, and that the conical 

 form permits many large eggs to be packed closely under the mother- 

 bird. But in dealing with organic forms, we should first try to in- 

 terpret them in terms of " the intrinsic forces of growth acting from 

 within and the forces of tension and pressure that may have acted from 

 without." The problem is : given a practically incompressible fluid, 

 contained in a deformable capsule, which is either (a) entirely inex- 

 tensible, or (b) slightly extensible, and placed in a long elastic tube, the 

 walls of which are radially contractile, to determine the shape under 

 pressure. An incompressible fluid contained in an inextensible envelope 

 cannot be deformed without puckering of the envelope taking place, and, 

 as this does not occur, it may be assumed (a) that the envelope is to 

 some extent extensible, or (b) that the whole structure grows under 

 relatively fixed conditions — two suppositions which are practically 

 identical with one another in effect. At all points the shape is de- 

 termined by the law of the distribution of radial pressure within the 

 given region of the oviduct, surface friction helping to maintain the 

 egg in position. If the egg be under pressure from the oviduct, but 

 without any marked component either in a forward or backward direc- 



* The Society are not intended to be denoted by the editorial " we," and they 

 do not hold themselves responsible for the views of the authors of the papers 

 noted, nor for any claim to novelty or otherwise made by them. The object of 

 this part of the Journal is to present a summary of the papers as actually pub- 

 lished, and to describe and illustrate Instruments, Apparatus, etc., which are 

 either new or have not been previously described in this country. 



t This section includes not only papers relating to Embryology properly so 

 called, but also those dealing with Evolution, Development, Reproduction, and 

 allied subjects. % Nature, June 4, 1908, pp. 111-13. 



