266 MEAD. [Vol. XIII. 



It represents four superimposed profile views of the ^g^ during 

 the first cleavage, drawn at intervals of about one minute. 



The division of the first two blastomeres is equal, simultane- 

 ous, and slightly oblique, so we have a 4-cell stage in which 

 the quadrants cannot be distinguished from one another. The 

 cross-furrows at the vegetative and animal poles are about 

 equal in length, and at right angles to each other, so that, as in 

 Amphitrite, two of the diagonally opposite cells are higher than 

 the other two. These four cells — the anlagen of the four 

 quadrants — divide simultaneously into eight cells by a right- 

 oblique cleavage (Figs. 90, 91), those of the anterior hemisphere 

 being slightly smaller than the other four. The next division 

 is synchronous and left oblique, and the resulting sixteen cells 

 are nearly equal in size. They soon divide obliquely to the 

 right, but not all exactly at the same time, though the corre- 

 sponding cells of the four quadrants, or, as Kofoid tersely 

 expresses it, "the cells of the same quartette," divide simul- 

 taneously: the upper quartette a^,^,, b^.^., ^,.,., d^.^., and that 

 at the vegetative pole, A^, B^, C^, D^, divide first ; next the 

 trochoblasts d'^', b^-^\ c'"'", d"' ; and shortly after d'-, b^-, c% d^\ In 

 Fig. 92 the first two quartettes have already divided, and the 

 two last are dividing. When these divisions are completed, 

 the egg is in a typical 32-cell stage, and the cells are of about 

 the same size, except the four larger at each pole. 



While the tgg remains in the 32-cell stage the polar globules, 

 which are still attached to the egg at the animal pole, usually 

 penetrate into the cells a^.^, b^.^, c^.^, or d^.^. They may enter 

 the same, adjacent, or even opposite cells, and rarely one 

 works its way between the cells into the segmentation cavity. 

 Curiously enough this phenomenon always takes place during 

 the 32-cell stage. 



The thirty-two cells all divide obliquely to the left, and the 

 corresponding cells in each quadrant divide synchronously. The 

 sequence of the quartettes is the same as in the previous genera- 

 tion ; but in case of sister cells the larger divides first. To be 

 more specific, the first cells to divide are a^.^, <5,.„, c^.^, d^,^ and A^, 

 B„ C„ D, ; then, a'-^ b'-\ c'-\ d'-' and a\ b\ c\ d' ; «'•'•^ b"-\ 

 c''\ d'-'' ; d\ b'-\ c'-\ d'-' ; a'-% b'-\ c'-% d'-' (cf. Figs. 93-97)- 



