6l8 FOOT AND STROBELL. 



EXPLANATION OF PLATE XXXVII. 



The photos, of this plate show the early stages of development of the male 

 and female pronuclei, four fixatives being represented. 



Photo. 23. Shows a transverse view of the second spindle, which has reached 

 the anaphase of development. Photo, taken by Dr. Fuller. Fixative, chromo- 

 acetic. Stain, alum-cochineal, x about 1000. 



Photo. 24. Vignetted section (3 fx) of mature egg, showing five of the eleven 

 chromosomes which have reached the inner pole of the second spindle, the aster 

 rays of which are still present. Fixative, 2% acetic. Stain, iron-haematoxylin. 

 X 950. 



Photo. 25. Section (3 \x) of mature egg, showing a little later stage of the 

 chromosomes than that of photo. 24. In this section only two of the eleven 

 chromosomes are seen. Within each tiny vesicle is a minute spherical body which 

 we interpret as the first appearance of a nucleolus. Fixative, picro-acetic. 

 Stain, iron-haematoxylin. X 660. The reproduction of this photograph is not 

 satisfactory. In the solar print the chromatin rings are nearly as sharp as those 

 shown in photo. 24, and on the inner side of each ring there is a tiny sharp 

 granule. 



Photos. 26-32 are vignetted sections (3 fx) of mature eggs, showing later 

 stages of development of the vesicles, from three to five vesicles in each section. 



Photo. 31 shows the second polar body on the periphery. 



Fixative, photos. 26 and 28, 2% acetic. X 660. Fixative, photos. 27, 29, 30, 

 and 32, chromo-acetic. x 660. Fixative, photo. 31, Flemming's fluid (strong). 

 Stain, iron-haematoxylin. x 660. 



Photo. 33. Section (3 \i) of mature egg, showing part of the head of the 

 spermatozoon breaking up into vesicles similar to those destined for the female 

 pronucleus, i.e., photos. 24-32. Fixative, picro-acetic. Stain, iron-haematoxylin. 

 X 660. 



Photo. 34. Vignetted section (3 /u) of mature egg, showing a later stage of 

 development of the male pronucleus than that of photo. 33. Only a part of the 

 pronucleus is present in this section. Fixative, chromo-acetic. Stain, iron- 

 haematoxylin. X 660. 



Photo. 35. A nucleolus from a germinal vesicle of an ovarian egg, showing 

 the presence of osmophile granules in an unstained preparation. Fixative, 

 chromo-acetic, followed by osmic acid, x 950. 



Photo. 36. The same nucleolus (at a slightly different focus) after the sec- 

 tions had been immersed for fifty-three hours in turpentine. Preparation still 

 unstained, x 950. 



Photo. 37. Spermatozoon showing spine, head, middle-piece, and tail. This 

 was taken from a slime tube in which the two cocoons were in process of forma- 

 tion. Spine and middle-piece only are stained. ^ 



