PRIMORDIAL UTRICLE. [ 537 ] PRIMORDIAL UTRICLE. 



whether it be merely a gelatinous investment 

 in its natural condition, or a true membrane, 

 because this formation, whether a membrane 

 or merely a layer of viscid protoplasm, exerts 

 in any case a special and most important 

 function. Among the principal reasons for 

 doubting the independent existence of a 

 pellicular nitrogenous membrane, are the 

 following facts : very young cells often 

 appear filled with a dense protoplasm (young 

 cells of antheridia of Cryptogamia, embryo- 

 sacs of many flowering plants, cells about to 

 produce zoospores in the Confervoids, &c.), 

 which may produce numerous new cells by 

 merely breaking up into separate portions, 

 and thus the function of the primordial 

 utricle is shared by the entire mass of 

 contents. Young cells of nascent tissues, 

 presenting this condition at first, acquire 

 the so-called primordial utricle afterwards, 

 simply by the dense contents becoming 

 excavated, as it were, as the cell-wall 

 expands, and following this in its growth, so 

 that the originally dense homogeneous mass 

 becomes a hollow sphere with the centre 

 occupied by watery cell-sap ; in other cases 

 the originally homogeneous protoplasm be- 

 comes excavated by numerous water-vesicles, 

 and thus honey-combed, until it forms a 

 mere reticulation of protoplasmic threads 

 upon the wall or stretched across the cavity. 

 But the point is by no means clear at present. 

 Indeed, the protoplasmic layer lying upon 

 the wall of the cell presents a complex 

 arrangement of parts in some cases: A. Braun 

 correctly distinguishes three layers in Hy- 

 drodictyon ; there are three in Chara, where 

 the intermediate one contains the chloro- 

 phyll-granules, and the inmost forms the 

 circulating mass ; a distinct layer is left 

 after the discharge of the zoospores in Cla- 

 dophora, &c. Pringsheim has lately asserted 

 that he has coloured blue by Schulz's 

 reagent, the outermost layer of the pellicular 

 structures detached from the cell-wall by 

 acids, &c. in the Confervae, and hence he 

 assumes that Mohl's primordial utricle is 

 really the most recently-formed of the layers 

 of cellulose belonging to the permanent cell- 

 wall, and that this is formed by a chemical 

 transformation of the superficial stratum of 

 the protoplasm. Possibly the last cellulose 

 layer of thickening may be brought away 

 from the wall by reagents, but it would 

 cause a confusion of ideas to call this the 

 primordial utricle, even if it be the pellicular 

 structure seen under some circumstances by 

 Mohl and others. The term properly applies 



to the formative stratum of all independently 

 vitalized masses of protoplasm, capable of 

 secreting layers of cellulose which in the cavi- 

 ties of parent-cells form layers of thickening 

 or septa, or, in a free condition, the primary 

 walls of new and independent cells. Thus, 

 as explained under the head of CELL-FORM- 

 ATION, the primordial utricle or formative 

 protoplasmic layer is the active agent in cell- 

 division, and the layer forming the surface of 

 the isolated portions of contents of parent- 

 cells produces the new cell-wall in all cases 

 of free cell-formation, whether taking place 

 in parent-cells, or, as in the case of the zoo- 

 spores of Algae, after escape from the latter. 



In many of the Algae, some of the indivi- 

 dual cells regularly exist for a certain period 

 as masses of protoplasm devoid of a cellulose 

 coat, as for example, the spores ofFucus and 

 its allies, and the active zoospores of Con- 

 fervoids ; and these bodies, although present- 

 ing a well-defined outline, do not appear to 

 have a properly developed membrane on the 

 surface, which merely appears to be denser 

 than the semifluid central portion. These 

 bodies withdraw themselves evidently from 

 the definition of a vegetable cell as ordinarily 

 given, and even the existence of a proto- 

 plasmic pellicle upon the surface of the 

 primordial utricle cannot be shown ; never- 

 theless they constitute all the essential living 

 part of a vegetable cell, and indicate most 

 clearly the undoubted fact, that the cellulose 

 walls, that is to say all the really solid and 

 permanent portions of vegetable structure, 

 are mere skeleton or shell for the protoplas- 

 mic or nitrogenous structures. Cohn has pro- 

 posed for the independently vitalized masses 

 of l cell-contents ' the title of primordial cells, 

 and they do correspond to many of the forms 

 of the ' cells ' of animal tissues, and of the 

 ' unicellular' animal organisms, AMCEBA, &c., 

 but none of these are really cells according 

 to the original idea : hence the transfer of 

 names causes confusion. Were not the 

 name nucleus already taken for the supposed 

 centre of vitality of those bodies, it would be 

 applicable, as would be that of cytoblast ; 

 but as these are occupied, the name of pro- 

 toplast, or as Huxley proposes, endoplast, 

 might be adopted, and certainly would be 

 preferable to calling the bodies " primordial 

 cells." 



The relation of the " primordial utricle " 

 or formative nitrogenous layer, to the SE- 

 CONDARY DEPOSITS of cell-walls, is not yet 

 clearly ascertained. Criiger has recently 

 asserted their essential agency in producing 



