or Mother Cell of the Sjpicule. 103 



been so neglected, that, in many instances, sponges have been 

 stated to contain, as distinctive characters, spicules which, 

 although widely differing in form and size from, are neverthe- 

 less the early stages only of the fully developed ones. 



So preeminently living is the s^rcode-cell about the ancho- 

 rates, that in getting them in particular to turn over, it is 

 frequently necessary to use considerable force to detach them 

 from the surface of the glass (fig. 15). 



3rd. A similar cell, about 7 by 4 GOOOths of an inch in dia- 

 meter, stretched over a single bihamate like parchment over a 

 dmm. Here the cell, being prevented from contracting beyond 

 the confines of the spicule, retains the transparency of its wall, 

 in which the granular, lenticular nucleus is perfectly visible 



4th. A similar cell (differing according to its developmental 

 size), from 2 to 10 GOOOths of an inch long, stretched over a 

 variable plurality of tricurvates. Here, too, the cell being pre- 

 vented from collapsing by the plurality of the spicule, and 

 its often lying crosswise (tig. 7), the transparency of the wall 

 remains, making the granular cytoblast or nucleus more 

 visible (figs. 5-9). 



Thus it would appear that all these cells are connected with 

 the production of the " flesh-spicules," and that therefore, with 

 the foregoing observations by Lieberkiihn, Schmidt, and my- 

 self, it may now be considered settled that the spicule does 

 originate in the interior of a cell. 



After the spicules have grown beyond the power of their 

 cells to contain them, the latter, which are still living, would 

 appear to allow them to pass through their parietes, without 

 rupture in the manner of sarcode-cells generally. What 

 becomes of these cells afterwards I know not ; but the number 

 of empty cells of the kind first described, with which the 

 Esperia may be charged, seems to point out that they have 

 either thrown off their spicules, have never had any, or are 

 going to produce more, or never will produce any. 



Clear, however, as it now is that the spicule originates in 

 a cell, the immediate origin is not known. That they all 

 commence from a minute cell within the parent one seems 

 to derive confirmation from the fact that they grow by the 

 extension of the central canal (in the flesh- as well as in 

 the s^e/eto«-spicule), on which the substance of the spicule is 

 deposited in concentric and therefore successive layers, which 

 central canal probably commenced in a single point or cell. 

 Indeed this is proved by the occurrence in some sponges of 

 globular or ellipsoidal monstrosities, where the natural form 

 of the spicule is exclusively long and linear. 



