34 CONK LIN. [Vol. XIII. 



Almost every writer on cleavage has a nomenclature of his 

 own, and not only must one learn a new system every time he 

 reads a new paper, but the difficulties of comparing the work 

 of one author with that of another become constantly greater 

 and greater. If it were possible to invent a system, as some 

 have attempted to do, which would be simple, convenient, and 

 universally applicable, it could, and of course would, be accepted 

 by every one who writes upon this subject ; but the differences 

 in cleavage are so great that such a consummation seems to 

 me almost hopeless. Besides, there are peculiar features in the 

 cleavage of every egg upon which nature seems to lay empha- 

 sis, and such features deserve some special recognition in the 

 nomenclature. Perhaps the most serious objection to any of 

 the systems of nomenclature which have been proposed is the 

 fact that it is almost impossible to recall cells by letters and 

 figures when they differ from each other only in the value of 

 one out of many exponents, e.g., it is practically useless for an 

 ordinary reader to attempt to remember the differences in the 

 position, shape, and history of the cells called ^"2 and b"'2 of 

 Blochmann's ('81) system, or d' and d'"^ of Wilson's ('92), 

 whereas it is comparatively easy to recall these cells if they 

 are known as the basal and terminal cells in the posterior arm 

 of the cross. It is not always possible to designate cells by 

 colloquial names which shall be of any help in forming a 

 mental image of them, but wherever it is possible it should be 

 done. At the same time some brief and accurate system of 

 nomenclature is necessary in order to show the derivation of 

 cells, and also for the purposes of comparison and reference. 



I have, therefore, concluded to employ, so far as possible, 

 a double system of names for every blastomere, one of which 

 shall be, if you please, its common name, the other its scientific 

 designation. Regarding the latter, which alone needs to be 

 mentioned in this place, I shall, in the main, follow Wilson's 

 system, given in his work on "The Cell Lineage of Nereis," 

 modifying it only to this extent, that the quartettes ^ of cells, 

 separated at various times from the macromeres will be desig- 



1 I use the term quartette, as employed by Kofoid ('94), to designate a group of 

 four cells of the same generation, one of which belongs to each of the quadrants 



