84 Papers from the Department of Marine Biology. 



CORRELATION OF THE DIFFERENT VARIATIONS. 



These observations and experiments furnished unmistakable evidence 

 of a high correlation of these variants in all three sea-urchins. From 

 table 3 the size of eggs and the percentage of eggs with jelly envelopes 

 maybe compared; also in table 4 the rate of membrane formation 

 and total cleavage. From the different experiments it was observed 

 that the following characters and characteristics were closely cor- 

 related, namely: 



No. 1. Globular shape of all or nearly all of the eggs. 

 No. 2. Large percentage of the eggs with the jelly envelope. 

 No. 3. Size of the eggs close to mode, with very Uttle variation. 

 No. 4. (a) FertiUzation membrane formed in about 2 minutes. 



(6) Large percentage of the eggs form a membrane. 

 No. 5. (a) A rapid rate of first cleavage. 



(6) A high percentage of cleavage. 



Vice versa, the following were closely correlated: 



No. 1. A large percentage of elliptical eggs. 

 No. 2. A low percentage of eggs with their jelly envelopes. 

 No. 3. Eggs usually larger than mode, and much variation. 

 No. 4. (a) Fertilization membranes slow to appear. 



(6) Small percentage of eggs form membranes. 

 No. 5. (a) Slow rate of first cleavage. 



(6) Low percentage of cleaving eggs. 



DISCUSSION. 



An adequate understanding of these variations can not be had 

 without a knowledge of the results of experiments with aging germ- 

 cells. It is expected that such results will appear in a later publica- 

 tion, but at present I wish merely to point out the nature of some of the 

 variants and to call attention to the marked range of differences in each 

 of the variants in fresh germ-cells. If these facts are thoroughly appreci- 

 ated, not only will many conflicting results on the physiology of eggs and 

 sperm disappear, but a clearer understanding of the situation may result. 



A number of investigators have remarked on the fact that under 

 apparently identical conditions varying experimental results were 

 obtained, and have suggested that the differences were due to some 

 physiologic difference in the eggs. 



Stockard (7) stated 'Hhe fact that a number of eggs when subjected 

 to the same solutions do not all respond in a like manner" was due to 

 "differences in individual resistance and vigor. "^ 



F. R. Lilhe (2) noted that ''the failure to obtain exactly the same 

 curve * * * was due in part to the natural variability of different 

 lots of eggs and sperm." Elsewhere he asserts that the percentage of 

 cleavage was more dependent on the conditions of the sperm than upon its 

 concentration. 



'All italics are mine. 



