1 8 BIOLOGICAL LECTURES. 



and the structure is therefore a true alveolar one in Biitschli's 

 sense ; indeed, Biitschli himself describes and figures the proto- 

 plasm of the Spkaerechinus egg as an example of that structure. 

 In Ophiura, however, the spheres measure up to 3.0 or 4.0 

 microns, and are undoubtedly " yolk-spheres " in the usual sense. 

 It is, however, quite certain from the ovarian development of 

 these eggs that they differ from the others only in degree, and 

 that Biitschli's criterion of size gives no satisfactory ground for 

 any real distinction. The alternative is to regard all the forms 

 as pseudo-alveolar, irrespective of the size of the alveolar 

 spheres, which are in all cases to be regarded as metaplasmic 

 bodies ; and this is the view which Reinke specifically applies 

 to Sphaerechimis. But if this view be adopted, we seek in vain 

 for any ground of distinction between such a fine " pseudo- 

 alveolar " structure as that of Arbacia, and the " true " alveolar 

 structure of tissue cells, and are forced to the conclusion that 

 in the latter case also the alveolar substance consists of passive 

 or metaplasmic material, a view which has in fact been adopted 

 by some writers. For my part, I am convinced that the entire 

 distinction is without adequate basis, and that no definite bound- 

 ary-line can be drawn between even the largest deutoplasm- 

 spheres, vacuoles, or other metaplasmic deposits, the alveolar 

 spheres of Arbacia or Toxopneustes, and those occurring in tissue- 

 cells; and probably all are, in the sense indicated above, to be 

 classed among the relatively passive or metaplasmic material. 



How generally the alveolar, reticular, or fibrillar formations 

 may occur is a matter still to be determined by observation. It 

 is probable that the alveolar structure will be found to be of 

 more general occurrence than has been supposed; and judging 

 by the appearance observed in echinoderm and other eggs, and 

 in coagulated albumen and other structureless proteids, I sus- 

 pect that some cases of so-called "reticular" formations will be 

 found to arise through the more or less imperfect fixation of 

 the alveolar, leading to the coagulation, contraction, and break- 

 ing down of the alveolar walls, 1 though I do not for a moment 

 mean to imply that such is the case with all reticula. 



1 It may be well to point out that Rhumbler has produced true fibrillar and 

 reticular formations in coagulated artificial gelatine-emulsions. 



