MATERIALS FOR A MONOGRAPH OF THE ASCONS. 537 



difficult to understand how Metschnikoff should have confused 

 them in contracted specimens. The youngest spicules are 

 figured by Metschniiioff in the middle of rounded granular proto- 

 plasmic masses, which become trefoil-shaped as the spicule 

 grows. There can be no doubt from his description that he 

 regards each of these protoplasmic masses as a single cell. He 

 appears, however, to have seen them only in the fresh state, 

 and in his figures no nuclei are shown; had he applied suitable 

 reagents, he would of course have found each of these masses 

 to be six cells, and not one only. It is a little strange he 

 should not have seen any cell outlines, but they are not very 

 obvious until the spicule has begun to grow and to cause the 

 cells to separate. In any case Metschnikoff was the first to 

 point out that the spicules '^always arise in the cell proto- 

 plasm, and not in the jelly-like ground substance. ^^ He does 

 not figure cells on the rays of the spicules, but the cell a on 

 pi. xxii, fig. 5, is obviously a spicule-cell detached from the 

 spicule (compare his description, p. 361). On the whole, I 

 think I may fairly claim that Metschnikofi'^s observations 

 confirm, or even forestall, my own, though his interpretation 

 of them requires modification. 



Polejaefl", in his work on the ' " Challenger " Calcarea/ 

 observed cells which he interpreted as scleroblasts on some of 

 the spicules, monaxon as well as triradiate (1883, p. 32). The 

 example which he figures (pi. vi, fig. 3, c.) is certainly very 

 remarkable in appearance, the result, perhaps, as the author 

 suggests, of preservation in alcohol. 



In 1885 Lendenfeld published a series of papers on Australian 

 calcareous sponges, which contain some observations on the 

 spicules and their origin. Of the spicules he states (1885 [2], 

 pp. 979, 980) that by prolonged action of gold-potassium 

 chloride the spicule splits into prisms "parallel to one 

 another, radiating from the axis.^' ''The radial structure 

 first makes its appearance in the interior, close to the inner 

 axis, which is a cylindrical chord of organic matter without 

 lime." "The inner part, the part produced first, of the spicule 

 is softer, and contains more organic matter, whilst the outer 



