104 Mr. H. J. Carter on the Origin of the Spicule and 



From what part of the mother cell this minute cell or point 

 comes, can hardly be conjectured. All that can be now said 

 on this point is, that the nucleus or cytoblast appears to be 

 entirely composed of a granular plasma, in which the granules 

 are of a uniform size and may afford the first points or cells 

 for the development of the spicules ; or this may be furnished 

 by the granular plasma of which the cell-wall itself is com- 

 posed. 



On the other hand, the final development and finishing of 

 the spicule must take place in the intercellular substance or 

 basal sarcode of the sponge ; for when even moderately de- 

 veloped, there is not a single sponge-cell large enough to 

 contain the spicule. Therefore, however clear it may be that 

 the spicule originates within a cell, that all-important inter- 

 cellular substance the basal, so-called " structureless," sarcode 

 must be viewed as the agent or " contractor " for the finishing 

 of the spicule as well as for the development of the whole 

 structure. 



I had often noticed, in my mounted specimens of Tethya 

 lyncurium {Donatia, Gray), that the minute stellates were in 

 a vacuole of the dried sarcode, and therefore concluded that 

 each must be formed in its proper cell. But, as Schmidt has 

 stated, the sponge must he fresh for the cells themselves^ to be 

 seen ; and the fresher it is, and the quicker viewed with the 

 microscope after the fragment for observation has been torn to 

 pieces, the better ; for the contraction of the living sarcode goes 

 on so quickly that after a little, especially as regards the 

 anchorates, the cell becomes so tightly wrapt round its con- 

 tents that it is hardly distinguishable. 



Again, I had often noticed that among the sheaf-shaped 

 bundles of minute linear spicules, which exist in many sponges 

 of different kinds, there seemed to be a passing of them into 

 the form of a tricurvate ; and when I saw Kolliker's figure 

 of conjectured spermatic filaments in Esperia (' Icones Histo- 

 logicaj,' Feinere Bau, 1864, pi. vii. f. 11), represented within 

 a nucleated cell, I also saw at once that these were spicules, 

 and concluded that the tricurvates were produced in like 

 manner. Now this is confirmed. 



As I have only found two examples of the occurrence of 

 the bihamate in its mother cell, and in each instance it was 

 single, I am not able to say that it also may not, in some 

 cases, be produced, like the tricurvates, in greater or less 

 plurality. We also know that the inequianchorates in Esperia 

 often abound in the form of "rosettes" — that is, where a 

 great number of them with their small ends inwards radiate 

 thus in all directions from a common centre. Here, I think, 



