No. 3] THE PROTOZOA AND METAZOA. 755 



tained by numerous observers that the so-called "achromatic 

 structures " of the mitotic-figure are primitively nuclear in 

 origin. (See O. and R. Hertwig ('93 and '96), Heidenhain ('94), 

 etc.) Furthermore, in the various kinds of Protozoa which have 

 been carefully studied the " achromatic " portions of the mitotic- 

 figures are developed from permanent, definite bodies which 

 are independent of the chromatin, although contained within the 

 cell-nucleus. As shown elsewhere in this paper, two apparently 

 similar elements of the metazoan cell have been described, 

 either or perhaps both of which may be comparable to these 

 intra-nuclear achromatic bodies in Protozoa. The first of these 

 is the " archoplasm " of Boveri ; the second is the substance 

 which forms the " centrodesmus " of Heidenhain, which is 

 described as a specific substance of the cell, as playing a 

 certain definite role in both resting and active phases, and as 

 distinct from the centrosome, from the nucleus, and from the 

 cytoplasm. Whether we consider this substance in the form 

 of "centrodesmus " or as archoplasm it appears, therefore, that 

 the cells of some Metazoa have a permanent specific substance 

 which may be considered the homologue of the "achromatic 

 body" of Protozoa. 



Boveri does not consider a nuclear origin contrary to the 

 conception of archoplasm, and with many others regards the 

 "achromatin" in many protozoan nuclei as archoplasm ('97). He 

 even holds it possible that there may be nuclei in Metazoa 

 which show a return to this primitive condition. Heidenhain 

 does not mention the derivation of the "centrodesmus" from 

 any other structure in more primitive forms. The only stand- 

 ards of identification are : its relation to the centrosome, the 

 formation of the spindle from its substance, and its permanency. 

 These same points may be used equally well for determining 

 the more primitive forms of archoplasm. 



In Noctiluca the so-called "sphere" surrounds the centro- 

 some at the period when the latter is unmistakable. Here, 

 also, the central-spindle is formed from the substance of the 

 sphere, and the latter is permanent in the cell, persisting as a 

 specific substance throughout all stages and quite distinct from 

 the cytoplasmic reticulum. The sphere in Noctiluca, therefore. 



