No. 3.] EGG OF ALLOLOBOPHORA FCETIDA. 549 



plasmic masses are scattered through the cytoplasm and on the periphery, and 

 smaller archoplasmic aggregations surround the sphere. This section shows that 

 much of the archoplasm which in the earlier stages is distributed through the 

 cytoplasm (Photos 51-54) is beginning to aggregate at the periphery, leaving 

 the rest of the cytoplasm relatively free from the substance (cf. these masses of 

 archoplasm with those in the ovarian egg, Photos 21 and 23, PI. XLI). Fixative, 

 corrosive sublimate. 



Photo 56, section (3 yu) through the cytoplasm of an egg at the same stage of 

 development as that of Photo 55; this section, however, is nearer the periphery. 

 It shows the same archoplasmic aggregations, but the configuration of the cyto- 

 plasm is quite different, due undoubtedly to the difference in fixation. The cyto- 

 plasm of Photo 56 resembles the living egg more closely, though the hyaline 

 spheres are larger than is usual at this stage. This suggests that the first effect 

 of the fixative on the cytoplasm may be to stimulate it to a more rapid develop- 

 ment. Fixative, Hermann's fluid without acetic acid. 



Photos 57 and 58, sections (3 m) through the cytoplasm of two eggs at the same 

 stage of development, i.e., fertilized mature eggs. The section of Photo 5S is very 

 near the periphery, showing the aggregations of archoplasm, v^'hich in Photo 57 

 are at the outer edge of the section. These eggs represent a later stage of devel- 

 opment than those shown in Photos 55 and 56 ; the second polar body has 

 been formed, and the chromosomes and sperm rod have reached the vesicular 

 stage. Fixative of Photo 57, picro-acetic, and of Photo 58, Flemming's fluid. 

 The picro-acetic does not preserve the form of the hyaline globules, which can be 

 seen distinctly in the living egg at this stage (cf. Photos (^^-11^ P'- XLIV, for fifteen 

 serial sections of an egg at about the same stage of development, i.e., pronuclei 

 just beginning to form). 



Photo 59, vignetted section (3 /i) of an egg, showing a later stage of development, 

 the pronuclei having increased in size and the archoplasm no longer scattered 

 around the entire periphery of the egg, is beginning to concentrate at two areas, 

 preparatory to forming the two polar rings. One of these areas is shown in the 

 photo. Successively later stages are shown in Photos 78, 79, and 80, PI. XLIV. 

 The hyaline globules in this section are larger than those seen in the living ec"' at 

 this stage. Fixative, Flemming's fluid without acetic acid. 



Photo 60, section (3;^) through the cytoplasm of the same egg shown in 

 Photo 51. This photo was taken to show the osmophile granules at this stage. We 

 have had to make a very light print of this, sacrificing a sharp differentiation of 

 the archoplasm, to avoid obliterating the granules. Near the center of the section, 

 the sphere at the lower pole of the first maturation spindle is faintly indicated. 

 In many eggs at this stage there are more osmophile granules than we have in this 

 section. The rapidity with which they fade depends upon the time the egg is left 

 in osmic acid, and the length of time the sections have been kept before exam- 

 ination. As this preparation was not examined for several months after fixation, 

 many of the smaller granules have undoubtedly faded {cf. Photo 61). Fixative, 

 Hermann's fluid without acetic acid. Preparation unstained and mounted in 

 glycerine. 



Photo 61, section (3/i) of a fertilized oocyte, first order, at the same stage of 

 development as the egg of Photo 54. Near the center of the photo is shown a 

 slight indication of a cross-section through the fertilization cone, near its apex. 



