476 Journal of Applied Microscopy. 



of the butterfly, they pass from the leucocytes into the epithelium, and the scale 

 mother-cells, either by becoming fluid, or by the amoeboid powers of the cell. 

 There is no penetration of the leucocyte into the scale, as stated by Mayer. 

 After this migration the fat globule changes chemically, so that there is less 

 reduction by osmic acid, and a brown instead of a black reaction is given. By 

 the end of the fifth day the wings are laid in folds, and the color pattern is defined. 

 The eleventh day after pupation, the globules pass into the scales, where they 

 break up into powdery granules, forming the definitive diffuse pigmentation of 

 the scales. E. M. Brace. 



Wilson, E. B. The Structure of Protoplasm. This is one of a series of lectures de- 

 Science. N. S.,10: 33-45, 1899- ^^^^^^^ at the Marine Biological Lab- 

 oratory at Wood's HoU. It is a study of the relation between the structure of 

 protoplasm and its vital activities, more especially as shown in the echinoderm 

 egg. Modern theories of protoplasmic structure are divided into two classes, 

 the first agreeing with Klein and Van Beneden, that protoplasm consists of a 

 reticulum imbedded in a homogeneous matrix ; the second, the view of Biitschli, 

 that it has an alveolar or emulsion-structure. Wilson, after studying the living 

 eggs of Asterias, Echinarachnius, Arbacia, and Ophiura, revises his earlier 

 opinions and agrees with Biitschli, that protoplasm in the resting cell is a mixture 

 of liquids in the form of a fine emulsion. Seen in sections, it appears to con- 

 sist of a meshwork of granules imbedded in a less deeply staining, continuous 

 substance, and within the meshes is a third homogeneous, slightly staining, 

 ground-substance. Studies on the living egg show that the appearance of the 

 meshwork results from the alveolar structure, the granules being due to coagu- 

 lation effects, and that all the elements of protoplasm, including the granules, 

 are liquid. The larger drops of the emulsion determine the alveolar structure, 

 and form the ground-substance in the spaces of the meshwork; the smaller 

 drops form the microsomes. Both of these lie in a homogeneous substance 

 which may really be an emulsion beyond the range of vision, for the limit of the 

 size of the drops is arbitrary, depending upon the power of the microscope. 

 There is reason to believe that the three parts of protoplasm are merely different 

 gradations of one structure, although the parts differ chemically, and in other 

 respects, in the same way as the larger masses to which they give rise. 



The coarser alveolar structure may be considered as secondary in origin, for 

 the young ovarian egg is a homogeneous mass in which the alveoli form later by 

 growth and differentiation. 



The astral rays are thought to be true branching fibrillae built up at the 

 expense of the continuous substance of the cell, and there does not appear to be 

 sufficient ground for believing that they arise from a specific archoplasm. 



It is difficult to make a sharp distinction between living and lifeless masses 

 in the cells, and the terms active and passive are substituted. The homogeneous 

 protoplasm may be composed of ultra-microscopic bodies, which produce the 

 visible elements by growth and differentiation. If we consider them as proto- 

 plasmic units, life must be considered, not as a manifestation of them, but of the 

 systems which they form. E. M. Brace. 



