28 



GEXEKAL SKETCH OF THE CELL 



i^ix'on.' In that classical object, the echinoderni-egg, for example, 

 it is easy to satisf}' oneself, both in the living cell and in sections, 

 that the protoplasm has a beautiful alveolar structure, exactly as 

 described by Biitschli in the same object (Fig. 1 1 ). This structure 

 is here, however, entirely of secondary origin ; for its genesis can 

 be traced step by step during the growth of the ovarian eggs through 

 the deposit of minute drops in a homogeneous basis, which ultimately 

 gives rise to the interalveolar walls. In these same eggs the astral 

 systems formed during their subsequent division (Fig. 12) are, I 



Fig. 12. — Section of sea-urchin egg {Toxopiieiistcs), li minutes after entrance of the sperma- 

 tozoon, showing alveoli and microsomes, sperm-nucleus, middle piece, and aster (about 2000 

 diameters). 



believe, no less certainly fibrillar ; and thus we see the protoplasm 

 of the same cell passing successively through homogeneous, alveolar, 

 and fibrillar phases, at different periods of growth and in different 

 conditions of physiological activity. There is good reason to regard 

 this as typical of protoplasm in general. Btitschli's conclusions, 

 based on researches so thorough, prolonged, and ingenious, are 

 entitled to great weight ; yet it is impossible to resist the evidence 

 that fibrillar and granular as well as alveolar structures are of wide 

 occurrence ; and while each may be characteristic of certain kinds of 



1 Wilson, '99. 



