THE NATURE OP CELL-ORGANS 2QI 



by new formation (as now seems to be the case with the centrosome), 

 the foregoing observations on the plastids give a substantial basis for 

 the hypothesis that protoplasm may be built of minute dividing bodies 

 which form its ultimate structural basis. It was these facts, taken in 

 connection with the phenomena of participate inheritance and varia- 

 tion (Galton), that led De Vries and his followers to the fundamental 

 assumption of " pangens," "plasomes," " biophores," and the like as 

 final protoplasmic units ; 1 but these were conceived not as the visible 

 granules, plastids, etc., but as much smaller bodies, lying far beyond 

 the limits of present microscopical vision, through the growth or 

 aggregation of which the visible structures arise. This assumption 

 has been harshly criticised ; yet when we recall that in one form or 

 another it has been accepted by such men as Spencer, Darwin, Beale, 

 Hackel, Michael Foster, Nageli, De Vries,. Wiesner, Roux, Weis- 

 mann, Oscar Hertwig, Verworn, and Whitman, and on evidence drawn 

 from sources so diverse, we must admit that despite its highly specula- 

 tive character it is not to be lightly rejected. In the present chapter 

 we may inquire how far the known facts of cell-structure speak for or 

 against this hypothesis, incidentally considering a number of detailed 

 questions of cell-morphology which have not hitherto found a place. 



A. THE NATURE OF CELL-ORGANS 



The cell is, in Briicke's words, an elementary organism, which may 

 by itself perform all the characteristic operations of life, as is the case 

 with the unicellular organisms, and in a sense also with the germ-cells. 

 Even when the cell is but a constituent unit of a higher grade of 

 organization, as in multicellular forms, it is no less truly an organism, 

 and in a measure leads an independent life, even though its functions 

 be restricted and subordinated to the common life. It is true that the 

 earlier conception of the multicellular body as a colony of one-celled 

 forms cannot be accepted without certain reservations. 2 Neverthe- 

 less, all the facts at our command indicate that the tissue-cell possesses 

 the same morphological organization as the egg-cell, or the protozoan, 

 and the same fundamental physiological properties as well. Like 

 these the tissue-cell has its differentiated structural parts or organs, 

 and we have now to inquire how these cell-organs are to be conceived. 



1 The following list includes only some of the various names that have been given to 

 these hypothetical units by modern writers : Physiological units (Spencer) ; gemmules 

 (Darwin); pangens (De Vries); plasomes (Wiesner); micella (Nageli); plastidules 

 (Hackel and Elssberg) ; inotagmata (Engelmann); biophores (Weismann); bioblasts 

 (Beale); somacules (Foster) ; idioblasts (Hertwig); idiosomes (Whitman); biogens (Ver- 

 worn); microzymas (Bechamp and Estor) ; gemma (Haacke). These names are not 

 strictly synonymous, nor do all of the writers cited assume the power of division in the 

 units. 2 Cf. p. 58. 



