2/4 THE PROTOZOA 



matic material," regarding which wide difference of opinion prevails. 

 If, with van Beneden ('83), Biitschli ('92), and many others, we assume 

 that the spindle in Protozoa arises by the local modification of the 

 protoplasmic network, we leave unexplained all of those division- 

 centres in Protozoa which are unmistakably permanent throughout 

 resting and active phases of the cell, and from which spindles are 

 formed (flagellates, Noctiluca, etc.). Nor can the interesting hypoth- 

 esis of Rabl ('89), even when supported by the evidence which 

 Heidenhain ('94), Biihler ('95), and Kostanecki ('97) have added, ex- 

 plain the facts in Protozoa, unless, indeed, it be assumed with Rabl 

 that the spindle fibres, never losing their identity, but merely modified 

 to form portions of the protoplasmic network, remain in Protozoa, in 

 the form of a compact and definite division-centre. Could Rabl's 

 suggestion be thus adapted, the result would be an hypothesis which 

 agrees essentially with the archoplasm theory of Boveri ('88). Boveri 

 maintained that the kinetic structures of the cell are derived from a 

 specific substance which he called archoplasm. At first ('88) he held 

 that the archoplasm, in the form of granules, is a permanent substance, 

 but in a subsequent paper ('95) he modified the theory by the sug- 

 gestion that the archoplasm might be distributed about the cell in the 

 form of a homogeneous material which cannot be readily demonstrated, 

 and which under the influence of the centrosome may be crystal- 

 lized out from the protoplasm. An essentially similar hypothesis was 

 formulated by Strasburger ('92) in connection with plant-cells. He 

 held that in these cells the protoplasm is composed of two essential 

 substances, one of which, the trophoplasm, is alveolar in structure and 

 is especially concerned with the processes of nutrition ; the other, 

 kinoplasm, is fibrillar in structure and is devoted to the formation of 

 the active portions of the cell, spindle fibres, cilia, flagella, and outer 

 cell-covering (Hautschicht). 



The facts in Protozoa fit in best with the archoplasm hypothesis. 

 Here, in a great many forms, is a definite structure composed of a 

 specific substance which, during cell-division, forms the spindle-figure. 

 Hertwig ('96) favored the view that the cytoplasmic and nuclear retic- 

 ula in the various phases which this portion of the protoplasm can 

 assume, are sufficient to explain the several division-centres, without 

 calling upon a special kinoplasm or archoplasm. He did not, how- 

 ever, in my opinion, give sufficient weight to the simpler division- 

 centres in Protozoa, but based his views upon the relatively complex 

 phenomena of division in Actinosphcerium. He believed that in this 

 form the spindle fibres and the pole-plates (which he homologized with 

 centrosomes of the Metazoa) are derived from the reticulum of the 

 nucleus. 1 No satisfactory explanation was given of the " Plastinge- 



1 Loc. cit., p. 59. 



