110 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



new aster grows, the old one gradually breaks down, and its substance is 

 probably used in the building up of the new system. 



In his later papers Boveri ('95) admits that the archoplasm may not 

 persist in the form of a definite body, but still may exist as a distinct 

 arclioplasmic substance distributed throughout the cell, or that it may 

 arise as a differentiation of the cytoplasm having no longer any connec- 

 tion with the reticulum. In Scolopendra at all early stages of mitotic 

 activity the archoplasm is in the second form, for while it still undoubt- 

 edly remains as a distinct substance, it is dispersed throughout the whole 

 cell. 



Nature of the Astral Systems. — It is the tendency of many of the 

 later workers upon the nature of the astral rays to regard them as the ex- 

 pression of cheinico-physical diffusion currents centring normally in the 

 centrosomes. This view was first expressed by Butsehli ('76), who in a 

 later paper ('92) expresses the opinion that the astral rays are merely 

 the optical sections of the walls of the alveoli which are arranged 

 around the centrosome in a radiating manner. Other workers upon 

 eggs in which an alveolar structure of the protoplasm is undoubtedly 

 present are inclined to adopt a similar or slightly altered view. Wilson 

 (:01'), in his papers on chemically fertilized eggs of sea urchins, has come 

 to the same conclusion, and Conklin (:02) has reached similar results in 

 Crepidula. Petrunkewitsch (:04), working principally upon Strongylo- 

 centrotns, also concludes that the substance of the astral rays " ist die 

 Substanz der Wabenwande; ein besonderes Archoplasma, oder Kino- 

 plasma, oder wie es audi heissen mag, existirt nicht, wenn auch eine 

 chemisch andere Beschaffenheit der ' Strahlen ' nicht ausgeschlossen 

 ist." 



All of these authors have worked upon material in which the struc- 

 ture of the protoplasm is of the coarse alveolar type, often distorted 

 and obscured by masses of yolk substance. It is evident that both of 

 these characteristics would tend to obscure the nature of the astral 

 rays if these were structural fibres. No convincing evidence has ever 

 been given that a special archoplasmic substance is not present at the 

 nodal points of the alveoli, while the presence of such material has 

 been maintained by many, notably by Boveri ('95) and by Wilson in 

 his earlier papers. In the more finely alveolar and in the so-called 

 reticular cytoplasm, such as occurs in the male cells of Scolopendra, 

 the astral rays are not so much obscured by other structures as in the 

 coarser form of protoplasm ; they appear as very fine, but in favorable 

 cases definite, filaments, which are entirely distinct from the true cyto- 



