100 PBOTOPLASM THEORY SINCE 1860 HACKEL. 



Radiolarien," in 1862, and other works, and summed 

 up in his " Generelle Morphologie," 1866. 



" The decisive and irrefragable proof that certain cells are 

 destitute of all traces of a membrane, and consist solely of a 

 little lump of semi-fluid mucilaginous cell-stuff (protoplasma), 

 surrounding a nucleus, was first given by me ; in that I ob- 

 served the penetration of solid particles into the substance of the 

 protoplasm, and their accumulation round the nucleus. This was 

 confirmed by the simple experiment of causing the amoeba- 

 like blood cells of invertebrates (Mollusca and Crustacea) to take 

 up pigment particles into their interior, by means of their 

 amoeba-like movements and changes of form" (vol. i., p. 271). 

 Having thus, like others, abandoned the cell wall, he still 

 clings to the nucleus, to which he attributes important powers. 

 But, in answer to Briicke, who insisted that many elementary 

 organisms existed which were destitute of nucleus, he is com- 

 pelled to admit the fact. And, in addition to the nucleated 

 cell, he admits another kind of elementary organism, which he 

 calls a cytod, or cell-like body, and which, in fact, is nothing 

 but a little mass of protoplasm. In 1866 he divides the plas- 

 tids, or morphological units of the first order, into cells i.e., 

 protoplasm with nucleus, and cytods, the same without 

 nucleus ; while both of these may exist with or without a cell 

 membrane. A mere lump of protoplasm is thus a naked cytod y 

 or Gymnocytod, under which head are classed the Protogenes, 

 the Protomceba, many monads, vibrios, &c. Under the head 

 of Lepocytods, or protoplasm masses with a membrane, but no 

 nucleus, are classed many Protista, such as certain Rhizopods, 

 many Alyce, the spores of Aphides, daphnidce, &c. To the 

 Gymnocyta, or naked cells i.e., protoplasm and nucleus be- 

 long many oya, the partition-products of the same, many nerve 

 cells, connective tissue cells, the escaped swarm spores of many 

 Algae, &c. To the Lepocyta, or the original cell with nucleus, 

 protoplasm and cell wall, belong most plant cells and many 

 animal cells. It is evident that, however valuable these precise 

 divisions may be as questions of natural history, the essentiality 

 of anything of even a twofold structure in the living unit is 



