CLEAVAGE IN THE EGG OF CEEEBRATULUS. 7 



VI. Experiment F (C lactetis). 



A series of pressure experiments was carried on with regard 

 to the localization problem. Incidentally I noticed a definite 

 modification in the cleavage of compressed eggs. 



When undivided egg is subjected to pressure between two 

 planes parallel to its vertical axis, the first cleavage plane passes 

 through the animal pole and always perpendicularly to the pressure. 

 The second cleavage plane is equatorial as Morgan observed in 

 Arbacia ('93, p. 148), giving rise to four cells of equal size} The 

 plane is, therefore, parallel to, but a little higher than, the third 

 cleavage plane of the uncompressed egg. If the pressure is relieved 

 from such eggs, the third cleavage takes place vertically, exactly 

 like the second of the ordinary egg. The subsequent history of 

 such eggs does not show any deviation from the normal cleavage. 



It is hardly necessary to state that, if the eg^ remains for some 

 time under a moderate pressure, the third cleavage planes appear 

 parallel to the first as has already been observed in compressed eggs 

 of other forms, giving rise to eight cells arranged in one plane. 



Vn. Experiment G {C. hicteus and C. ^narg hiatus)-. 



Eggs were fertilized artificially as in other experiments. The 

 moment the first cleavage constriction was to appear, they were shaken 

 so as to remove their membrane and were transferred^ into Ca-free 



1 In passing it may be pointed ( nt that C. B. Wilson ('00) seem-; to have made his 

 observation on the compressed eggs of C. hictcust, judging from his figure (PL 10, Fig. 52) and 

 statements that the second cleavage is horizontal and the third vertical (pp. 146-147). 



2 This experiment was carried out primarily for some other purpose in the summer of 

 1904 and was repeated with the same result in the spring of 1906. 



3 It was not easy to transfer eggs alone into Ca-free seawater ; always a little ordinary 

 seawater went in with ihe egg. In this experiment* they were, as a matter of fact, kept in 

 the seawater with diminished amount of calcium. I mention this expressly because in 

 using pure Ca-free seawater the result may be different. 



