730 



SCIENCE 



[N. S. Vol. XXXIX. No. 1011 



A description of detailed experiments will ficially adhering water. Following the deter- 

 mination of the fresh weight, the material was 

 reduced to absolute dryness in vacuo over 

 PjOj. The results of two series of weighings 

 given in Table I. are: 



soon appear. 



Chas. B. Lipman 

 Eeseakch Laboratoet roE Soils, 

 Univeesity op Caufoenia 



the water content of the embryonic 



nervous system 

 Growth and morphological differentiation 

 go hand in hand in the developing organism, 

 but obviously growth alone can not lead to an 

 increase in the complexity of form without 

 itself being differential. The various tissues 

 and organs of the embryo, however, do grow at 

 different rates, and since, in general, rate and 

 extent of growth are measurable in terms of 

 the rate and extent of water absorption, it 

 follows that differential growth must depend 

 on the ability of the embryonic tissues to ab- 

 sorb and hold, relative to their dry substance, 

 different amounts of water. That this must 

 be true at some period in development follows 

 from the comparative dry substance deter- 

 minations familiar to every one, but how early 

 in the ontogeny differential absorption occurs 

 has not been known, although its importance 

 as a factor in morphological differentiation 

 has been hinted at often enough. 



My investigation of this question was begun 

 on the embryos of Bana pipiens in the spring 

 of 1913. The methods employed were tedious 

 but simple. In one series of experiments eggs 

 were allowed to develop normally until a time 

 when the body of the embryo could be cut 

 from the yolk by means of a very thin knife. 

 The division was accomplished easily with a 

 minimal loss of material. Unfortunately the 

 various tissues in the separated portions can 

 not be isolated, but even if this were possible, 

 an unavoidable error due to the presence of 

 considerable quantities of yolk within the cells 

 of the nervous system would remain. How- 

 ever, at the stage of development under con- 

 sideration, it is safe to assume that the opera- 

 tion results in the separation of two masses, 

 one of which is predominantly yolk, the other, 

 predominantly nervous tissue. 



The separated masses were carefuUy weighed 

 in closed vessels after removal of the super- 



TABLE I 



{Hana pipiens) 



Control observations on embryos of Arribly- 

 stoma punctatum were then made, but, owing 

 to technical difficulties, it proved easier to 

 compare the water content of the nervous 

 system with that of the entire embryo rather 

 than with that of the tissues constituting the 

 yolk sac. The results of these preliminary 

 determinations were as follows: 



TABLE II 



(Amblystoma larvffi) 



These figures may serve as a basis for com- 

 parison with the water content of the nervous 

 system. As Table III. shows, the values for 

 the latter are identical with those for the 

 frog- embryo, and belong to an order of magni- 

 tude quite different from the values for the 

 larval body taken as a whole. 



Comparing these values with the corre- 

 sponding ones found for the frog embryos, we 

 may say, within the limits of error, that the 

 larval nervous system of these amphibians is 

 a tissue which contains 80 per cent, of water 

 and 20 per cent, of dry substance. 



