524 B. A. HINCHIN. 



Banyuls the growth of the large monaxous of the species 

 termed by me Clathrina, sp. dub., but did not succeed in 

 finding the earliest stages. In the youngest stage found 

 the spicule bore three cells, two fusiform cells attached to 

 the shaft, and a branched cell at the extreme apex of one 

 end, apparently the proximal end. The two cells on the shaft 

 each closely resembled a basal formative cell on the ray of a 

 triradiate system, and the cell at the extreme tip resembled an 

 apical formative cell. A later stage had five cells, four on the 

 shaft and one at the apex. A still later stage had the apical 

 cell and a number along the shaft, but it was difficult to deter- 

 mine exactly how many on account of the great size of the 

 spicule (PL 39, fig. 20, spic. monax.). 



The stage with five cells is obviously to be derived from the 

 stage with three by division of each of the two cells applied to 

 the shaft in the earlier stage. This suggests that the stage 

 with three cells is derived in a similar manner from a stage 

 with one cell on the shaft and one at the apex; this would be 

 a state of things exactly comparable to what is found ordinarily 

 on the ray of a triradiate, with its basal and apical formative 

 cell. The huge monaxons would then be formed just as a 

 single ray of a triradiate system, with the difference that the 

 basal formative cell repeatedly divides to furnish a row of cells 

 which build up the spicule. In this connection we may refer 

 to the interesting lines of growth described by Ebner (1887, 

 PI. 41, figs. 51 — 53) in the large monaxon spicules of Leu- 

 candra alcicornis and aspera, each system of lines being 

 probably referable to a separate secreting cell. 



Many of the large monaxons in Clathrinidse, on the other 

 hand, are almost certainly not true monaxons, but derived 

 by modification of a triradiate system (cf. Haeckel, 1872, 

 p. 350). In this way one can distinguish true or primary 

 monaxons from what may be termed secondary monaxons. A 

 good instance of the latter is to be found, probably, in the 

 large elbowed monaxons in the stalk of Clathrina lacunosa. 

 I have long had a belief that the large monaxons found in 

 Clathrinidse would turn out to be in all cases secondary 



