No. 3.] THE EGG OF VIRBIUS ZOSTERICOLA. 743 



Type I. — The spindles of the nuclei in the 2-^-cell stage are 

 parallel to each other and the " cross-ftirrows " are perpendicular 

 to each other {PL XXXVII, Fig. y). 



In this type of segmentation, after the nuclei have divided, 

 the first cleavage-furrow becomes bent at the points where the 

 second furrow is about to appear and forms two " cross-fur- 

 rows " which are perpendicular to each other (PI. XXXVII, 

 Fig. 7). The second plane then appears, not as one continuous 

 meridianal plane dividing the two blastomeres, but the portion 

 dividing one half of the Qgg lies somewhat inclined to that 

 dividing the other. 



While the second cleavage-plane is forming there is a change 

 in the position of the major axis of the Qgg in relation to the 

 first cleavage-plane. Just before the second plane is formed 

 the major axis is, in most cases, perpendicular to the first 

 plane (PI. XXXVII, Fig. 7), but as the second plane appears 

 the shape of the egg changes, and the major axis is no longer 

 perpendicular to the first plane, but takes the direction shown 

 in PI. XXXVII, Fig. 9. 



Type II. — The spindles of the miclei in the Z-zf-cell stage are 

 parallel to each other and the " cross fnrrows " lie parallel to each 

 other in the major axis of the egg (PI. XXXVII, Fig. 8). 



The only difference between eggs which develop according 

 to this type of segmentation and those which develop accord- 

 ing to Type I is in the position of the "cross-furrows." In 

 this type the "cross-furrows " are parallel to each other and in 

 the major axis of the egg (PI. XXXVII, Fig. 8), so that the 

 lateral blastomeres are in contact on both sides of the egg 

 (PI. XXXVI, Fig. 10), instead of the alternate arrangement of 

 Type I (PI. XXXVII, Fig. 9). 



Type III. — The spindles of the miclei in the 2-^-cell stage are 

 perpendicular to each other {PI. XXXVII, Fig. 6). 



In this type the planes dividing the two blastomeres are 

 meridianal, but lie at right angles to each other (PI. XXXVII, 

 Fig. 11). There is no change in the first furrow, or in the 

 direction of the major axis of the egg. 



