132 PROCEEDINGS OF THE ACADEMY OF [March. 



from each of the four macromeres of the normal egg. If the yolk 

 has divided once so as to form two macromeres, each of these may 

 give rise to three micromeres, having the characteristics of the three 

 quartet cells of the normal egg. In short, the number of micromeres 

 depends upon the number of macromeres: when there are four of 

 these as in normal eggs, the micromeres are formed in three quartets; 

 when there are two, they are formed in three pairs; when there is 

 but one macromere, i.e., when the yolk remains undivided, the 

 micromeres are formed singly. 



11. When eggs are subjected to pressure the third cleavage which 

 normally gives rise to the first group of micromeres, may divide one 

 or more of the macromeres equally, thus giving rise to five, six, seven 

 or eight macromeres. If the pressure is removed from such eggs 

 each macromere gives rise to three micromeres in a manner approxi- 

 mately normal ; again showing that the number of micromeres which 

 may come from a macromere is fixed, whatever the number of 

 micromeres may be. 



12. The results stated in the two preceding paragraphs show that 

 the omission or the addition of cleavages does not alter the character 

 or localization of the egg substances and that the latter, when unim- 

 peded, determines the character of the cell division. 



13. Isolated blastomeres undergo partial development, each giving 

 rise only to the cells which it would form if still a part of the entire 

 egg, but the general form is entire, i.e., there is no open side. 



14. A weak electric current leads to the solution and disappearance 

 of the chromatin and may destroy spindle fibres and astral rays, 

 thus stopping mitosis. It may also destroy the polarity of the cell 

 and prevent the normal separation of protoplasm and yolk. 



15. Abnormalities of mitosis may perpetuate themselves in sub- 

 sequent divisions, even when the cause which first induced them is 

 removed. 



Carlotta J. Maury, Ph.D.: "A Contribution to the Paleontology 

 of Trinidad." Illustrated by drawings and charts.* 



A large number of basal Eocene species recently discovered in the 

 vicinity of Trinidad Island are described. 



These fossils have a very significant bearing on the problem of 

 the origin of the Midwayan and Lignitic faunas of the Gulf and of 

 certain species found also in lower Eocene formations of the Atlantic 

 coast of the southeastern States. 



The shells were discovered by Mr. Arthur C. Veatch while explor- 

 ing a small island called Soldado Rock. This lies off the south- 

 western end of Trinidad, in the Gulf of Paria, near the Serpent's 

 Mouth, and rises about 100 feet above the surrounding waters. On 

 this rock Mr. Veatch found a succession of eight beds of which Nos. 

 2, 6 and 8 were fossiliferous. The collections made by Mr. Veatch 

 were given to the writer for identification. 



Bed No. 2 was found to contain a rich fauna of basal Eocene forms, 

 among the forty-four species being the exceedingly characteristic 



