330 PROCEEDINGS OF THE ACADEMY OF [April, 



Maturation and Fertilization. 



It is not the purpose of this paper to discuss in detail the maturation 

 processes of the egg, but a few words in that connection may not be 

 amiss. Maturation appears to have begun at the time of laying, since 

 the first polar spindle is already formed in all eggs examined. In 

 fig. 1 the chromosomes have moved to opposite ends of the first matu- 

 ration spindle, and at a slightly later period, fig. 2, the sperm may be 

 seen making its way through the yolk globules toward the upper pole. 

 In a large number of sections examined the sperm is seen to have 

 entered at some point below the equator of the egg, though apparently 

 never directly at the center of the vegetative pole. The chromatin 

 of the sperm nucleus is but shghtly evident at this time, but astral 

 radiations are strongly marked in the surrounding cytoplasm. The 

 clear more protoplasmic substance of the egg becomes aggregated 

 principally around the first polar spindle and in the neighborhood of 

 the sperm nucleus, though long strands of finely granular protoplasm 

 extend through nearly the entire egg, forming the astral rays. The 

 yolk, which is in the form of rather small yolk globules, encroaches 

 closely upon these centers, but is not, as a rule, found within them. 

 As the first polar body arises, the upper surface of the egg becomes 

 distinctly indented immediately above the first polar spindle and from 

 this depression the first polar body emerges, bearing with it the distal 

 end of the first maturation spindle, which rises as a whole toward the 

 upper surface of the egg. During this process the sperm nucleus and 

 aster remain in relatively the same position as before. There appears 

 to be no telophase to this division, but without entering into a rest stage 

 the second polar body is given off. This arises from the same place as 

 the first, pushing the latter farther outward or somewhat toward the 

 side (PI. XXI, fig. 3), Both finally lie in the slight depression at the 

 surface of the egg. The female nuclear elements still left within the 

 egg then come to rest, at first lying closely against the cell wall below 

 the polar bodies. The first polar body does not divide again immedi- 

 ately and may never do so, though usually at a later period three are 

 found. If it remains undivided the first polar body exceeds the second 

 in size. 



With the close of maturation the sperm nucleus is seen to have moved 

 upward through the yolk; its chromatic elements have become more 

 evident several large nucleoU being present. The same is true of 

 the female pronucleus. They now approach each other, and come to lie 

 with their nuclear walls closely appressed (fig. 4), the egg nucleus U-ing 



