300 W. G. Van Name— Embryology of Easlylochus. 



Fig. 33. — Embryo about eight days old endeavoring to escape through an open- 

 ing accidentally torn in the egg membrane. Ventral surface of embryo 

 shown. X 285. 



Fig. 33. — Embryo about eight days old, prematurely hatched by teax-ing the egg 

 membrane, x about 285. 



Fig. 34.^ — -Embryo a few days after hatching, x about 285. 



Fig. 35. — Embryo a week after hatching, x about 285. 



Plate XLI. 



Fig. 36. — Planocera nebidosa. Uterine egg showing a first polar spindle. This 

 is ijeculiar in that all the chromosomes have already assumed the elongated 

 form, the rings having broken at one point. A jiart of the spermatozoon is 

 seen to the right of the spindle, x 860. 



Fig. 37. — Planocera nebidosa. Beginning of the second polar sjiindle. In this 

 specimen the centrosomes are separating in a direction nearly transverse to 

 the axis of the spindle, x 860. 



Fig. 38. — Planocera nebidosa. Egg in a little earlier stage than the last, yet the 

 second polar spindle is further advanced. Near it is the sperm-nucleus, in 

 this case rather larger than usual at this sta^e, and in the upper right hand 

 part of the section the sperm-aster, whose centrosome appears very large 

 owing to insufficient exti'action of the stain with the alum solution. • x 860. 



Fig. 39. — Planocera nebidosa. Sperm iiucleTis and aster from an egg in the 

 second polar spindle stage. The centrosome has just divided, and the cen- 

 trosphere has become elongated, x 1240. 



Fig. 40. — Planocera nebulosa. Second polar spindle more advanced than in fig. 

 38. Most of the chromosomes lie in another section. Near the spindle the 

 sperm-niicleus, and to the left, near the edge of the section, the sperm-aster 

 is shown. The latter has proceeded somewhat farther in its division than 

 the one shown in fig. 39. x 860. 

 Note. — Figs. 36, 38 and 40 show the position of the spermatozoon and later 



the sperm-nucleiis very near the center of the egg and the polar spindles, which 



is so common in this species as to be quite characteristic. 



Fig. 41. — Planocera or Eustylochus. Diagram showing successive stages in the 

 division of a chromosome of the first polar spindle. 



Fig. 42. — The same, showing another method of division. 



Fig. 43. — Diagram showing different degrees of modification (not different stages, 

 as in the last two figures) of one of the forms of chromosome of the first 

 polar spindle. 



Fig. 44. — Eustylochus ellipHcus. Entire egg in two cell stage, x 285. 



Figs. 45 and 46. — Same in four and eight cell stages respectively, seen from the 

 vegetative pole, x 285. 



