June 19, 1908] 



SCIENCE 



945 



external conditions. If either is altered 

 the result is an interference with ideal 

 heredity, which may be defined as identity 

 in process of development between parent 

 and offspring. These two conditioning 

 factors of heredity are of equal potency, 

 since each is efficient only in the presence 

 of the other. 



The Bate of Growth of the Egg-yolk in the 

 Chick, and the Significance of White and 

 Yellow Yolk in the Ova of Vertebrates: 

 OscAE Riddle, The University of Chi- 

 cago. 



A method has been found by which the 

 rate of growth of the egg-yolk of the chick 

 may be easily measured. If the fat-stain 

 Sudan III. be fed to laying hens at in- 

 tervals of one, two or more days, the stain 

 can be found later in the form of concen- 

 tric red rings in all of the rapidly growing 

 ova. The actual rate of growth varies 

 widely— to 2 mm. ; but one day of growth 

 normally includes a layer of white yolk 

 and a layer of yellow yolk. It is probable 

 that the layer of white yolk represents the 

 part which is grown during the later hours 

 of the night, and that the yellow yolk is 

 yolk of more rapid growth produced dur- 

 ing the remainder of the day. 



In the turtle's egg there is a concentric 

 layer of white and another of yellow yolk 

 for each of the four years required (Agas- 

 siz) for the complete growth of these ova. 

 Here the yellow yolk undoubtedly corre- 

 sponds to a part of the egg which is rapidly 

 grown. 



A consideration of the formation and 

 arrangement of white and yellow yolk in 

 the ova of the several groups of vertebrates 

 leads to the conclusion that everywhere 

 among these animals white yolk is yolk of 

 relatively slow growth, and that the yellow 

 yolk is yolk of more rapid formation. 



For the more intimate explanation of 

 the concentric layers, etc., of white yolk 



one must take into account two factors 

 which seem to have been overlooked, name- 

 ly, the reversible aetion of enzymes which 

 in periods of hibernation or low feeding 

 must tend to analyze and break up the 

 large yolk granules at the periphery of the 

 yolk; at the same time some of the newly 

 formed products of decomposition will 

 leave the peripheral part of the ovum and 

 become distributed between the latter and 

 the surrounding circulating blood accord- 

 ing to the requirements of the partition 

 coefficient of each of these substances. 



The remarkable arrangement, and ap- 

 parent elaborate organization of some of 

 the most prominent morphological elements 

 of the larger egg-ceUs thus receive their 

 physiological explanation. 



A Comparison of the Reactions of a Ter- 

 ranean and a Subterranean Species of 

 Isopod: A. M. Banta, Marietta College. 

 An investigation of the faima of iVIay- 

 field's cave near Bloomington, Indiana, 

 suggested the desirability of studying the 

 reactions to various stimuli (light, tactile 

 stimuli, etc.) of some cave species in com- 

 parison with the reactions to the same 

 stimuli of a near relative living in other 

 situations. The blind cave isopod Cceci- 

 dotea stygia, and the common asellid, Asel- 

 lus communis, were selected. 



It was desired to determine if the in- 

 creased development of tactile organs in 

 cave animals was accompanied by an in- 

 creased sensitiveness to tactile stimulation. 

 The experiments proved this conclusively. 

 A second point was to determine the rela- 

 tive sensitiveness of the two animals to 

 light. The cave species proved to be very 

 little sensitive to light compared with its 

 outdoor relative. With directive light the 

 threshold of stimulation was about 2.2 

 candle-meters with Asellus and about 80 

 candle-meters with Ccecidotea. It was also 

 desired to find out, if possible, what were 



