PART II. THE CYTOLOGY OF THE EGGS OF CIDARIS 

 TRIBULOIDES AND OF CROSS-ACTIVATED 



CIDARIS EGGS. 



Structure of the Cidaris Egg. 



The living eggs of Cidaris are about 0.07 mm. in diameter. They 

 are very transparent and the various phases of the nucleus during 

 division may be followed readily. Because of the transparency of 

 the living egg, I was much surprised to find that in the stained sections 

 the cytoplasm was filled with deeply staining spherules (plate 1, a 

 to e; plate 2, A and b). As this seemed at first a somewhat unusual 

 feature in a sea-urchin egg, sea-urchin eggs often being described as 

 alecithal, a somewhat prolonged study of these spherules has been 

 made. My conclusions concerning them have been reached in part 

 indirectly, through the examination of other sea-urchin eggs which 

 were available for study by the aid of various micro-chemical methods. 

 My own study has been based on the eggs of Arbacia punciulata, 

 Echinometra mathcei, Peronella lesueri, and Salmacis alexandri, 

 while that of one of my students, Dr. Hope Hibbard, has been based 

 on EchinaracJmius parma. 



The spherules in Cidaris measure from 0.2 to 2 microns in diameter. 

 With iron haematoxylin they stain intensely black. During the 

 resting stage of the nucleus the spherules are scattered uniformly 

 through the cytoplasm from nuclear wall to the surface of the egg, 

 the surface layer being filled with deeply staining microsomes. 

 With the transition from the ''resting stage" to the active phases of 

 cell life as exhibited in mitosis — i. e., with the passage from the gel 

 to the sol phase in the protoplasm — the spherules are carried out from 

 the region of the nucleus, so that when the amphiaster is established it 

 lies in a region of clear cytoplasm, one entirely free from the presence 

 of the spherules described (plate 1, fig. a). 



Some eggs are characterized by a smaller number of large spherules, 

 other eggs by a larger number of smaller spherules. After the 

 elimination of the possible explanation that the difference in size 

 might be due to different degrees of extraction of the stain, an 

 attempt was made to show a correlation between size of spherules 

 and phase of division, a preliminary examination having shown that 

 most of the eggs in the anaphase of the first division had large 

 spherules. It was soon found that such a generalization would be 

 without adequate basis in fact, since numerous exceptions to the 

 supposed condition were found (plate 2, figs, d to l), and it may be 

 stated positively that there is no correlation between the primary 

 size of tliese deutoplasmic spherules and phase of division. As the 



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