BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
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., IL, 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. 
arch. Archenteron. gib. pol. Polar globule. 
ast’cal. Astrocoel. pd. Foot. 
bl’ po. Blastopore. prc, ame. Amocboid process. 
bl’po. a. Anterior end of blastopore. prj. vel. Velar projections. 
bPpo. p. Posterior end of blastopore. spa. Vel, Intercellular space. 
cav. sy. Cleavage (or segmentation) spa. Ins. Lenticular space. 
cavity. vac. Vacuole. 
ench. Cells destined to form the US, ce. Head vesicle. 
shell gland. 
