323 KEPOJtTS ON THE STATE OF SCIENCE. 



D. Hence, assuming that tlie permeability of the egg and embryo is 

 the same as that of the tadpole, it follows that the increased osmotic 

 pressure cannot be I'egarded as the cause of the persistent yolk- plug and 

 open medullary groove. 



F,. This conclusion is confirmed by the results of some ' desiccation ' 

 experiments. 



As soon as the dorsal lip of the blastopore had appeared, the jelly of 

 the eggs was allowed to dry up to such an extent that the eggs became 

 strongly flattened against the glass slide on which they were placed, and 

 assumed the form of a plano-convex lens. 



Nevertheless, development continued, and bofh blastopore and medulla 

 closed. 



F. It seems highly probable that the embryo does not need to absorb 

 water from outside during the closure of the blastopore. 



II On the Symmetry of the Egg aiid the Symmetry of the Embryo. 



Thvi controversy in which Eoux, Hertwig, and others have been 

 engaged, as to the exact relation between the first furrow and the sagittal 

 plane, hardly needs recalling. It is also well known now that the problem 

 demands a knowledge of the position in each of a large number of eggs of 

 not merely these two planes, but of the sperm-path and the plane of 

 symmetry of the unsegmented egg as well. An attempt has been made 

 to acquire a sufficiently large number of observations. 



(«) The positions of the plane of symmetry, first furrow, and 

 sagittal plane have been accurately determined in a considerable number 

 of eggs. The result is — 



(1) There is a tendency for the first furrow and the sagittal plane to 

 coincide, but there is no correlation between them. 



(2) There is a much stronger tendency for the sagittal plane to lie in 

 the plane of symmetry, and a considerable correlation between then). 



(3) The first furrow tends to lie either in or at right angles to the 

 plane of symmetry. 



(/3) The plane of symmetry is itself said to be determined by the point 

 of entry and path of the spermatozoon. 



Observations are now being made with a view to ascertaining the 

 correctness of this view and the correlations between sperm-path, plane 

 of symmetry, and first furrow. 



III. Experiments have been begun on the possible influence of the 

 direction of light or heat in determining the deviation of the sagittal 

 plane from the plane of the first furrow. As far as they go they seem to 

 show a tendency of the sagittal plane to lie either in or at right angles 

 to the direction of the incidence of light (or heat). 



It is proposed to continue these experiments with light of various 

 colours, and also to institute a series of investigations into the effect of 

 light upon the development of the egg and embryo. For these reasons 

 the Committee ask to be reappointed, with a renewal of the grant. 



