STRUCTURAL BASIS OF THE CELL 293 



a large part even of this substance may be lost in the process. The 

 term "persistent organ" is therefore used, in rather a figurative sense, 

 and if too literally understood may easily mislead us. 



With the foregoing considerations in mind let us turn to the actual 

 structural relation of the cell-organs. 



B. STRUCTURAL BASIS OF THE CELL 



In Chapter I. some of the reasons have been given for the conclu- 

 sion that none of the obvious structural features of protoplasm (fibrillae, 

 alveoli, granules, and the like) can be regarded as necessary or uni- 

 versal ; and we may now inquire whether there is any evidence that 

 such structures may have such a common structural basis as De Vries's 

 theory assumes. I shall here take as a point of departure my observa- 

 tions on the structure of protoplasm in echinoderm-eggs, already briefly 

 reviewed at page 28. The beautiful alveolar structure of these eggs is 

 entirely of secondary origin, and all the visible structural elements 

 arise during the growth of the eggs by the deposit and subsequent 

 enlargement of minute spherical bodies, all apparently liquid drops, 

 in a homogeneous or finely granular basis which is itself a liquid. 

 Some of these spheres enlarge to form the alveolar spheres, while the 

 homogeneous basis or continuous substance remains as the interalve- 

 olar material. Others remain much smaller to constitute the " micro- 

 somes " scattered through the interalveolar walls ; and these bodies, 

 like the alveolar spheres, are perfectly visible in life, as well as in 

 section ; they are therefore not coagulation-products or artifacts. From 

 these three elements arise all the other structures observed in these 

 eggs, deutoplasm-spheres (Opliiura) and pigment-bodies (Arbacia) 

 being formed by further enlargement and chemical alteration of the 

 alveolar spheres, while astral rays and spindle-fibres are differentiated 

 out of the inter-alveolar material and microsomes. 1 These various 

 elements show a continuous gradation in size from the largest deuto- 

 plasm-spheres down to the smallest visible granules, the latter being 

 the source of all the larger elements, and in their turn emerging into 

 view from the " homogeneous " basis. Clearly, then, none of these 

 bodies can be regarded as the ultimate structural units ; for the latter, 

 if they exist, must lie in a region at present inaccessible to the micro- 

 scope. This fact, however, no more disproves their existence than it 

 does that of molecules and atoms. It only shows the futility of such 

 attempts as those of Altmann and his predecessors to identify " gran- 

 ules " or "microsomes " as final morphological units, and compels us to 

 turn to indirect instead of direct evidence. It may, however, again be 

 pointed out that it would be quite irrational to conclude that the small- 



1 r/ Wilson, '99. 



