118 



bulletin: museum of comparative zoology. 



EXPLANATION OF THE PLATES. 



All figures were drawn from the eggs of Agriolimax agrestis, L., and are from 

 preparations unless otherwise stated. A camera lucida was in every case employed. 



A, B, C, D, denote the first four cleavage spheres, A and B corresponding to 

 the anterior quadrants, B and C to the right quadrants of the embryo. For the 

 meaning of a, b, c, d, with their exponents, consult the explanation of the system 

 of nomenclature of cells to be found on pages 40-43. 



The first, second, and third cleavage furrows are indicated by the Roman 

 numerals I., II., III., respectively. 



Arrows are used to show the common origin of the cells thus connected, the 

 head of the arrow occupying the cell nearer the animal pole of the egg. 



ABBREVIATIONS. 



