STUDIES IN .SPICULE FORMATION. 33 



spicules (wLicli do not seem to have been previously described) 

 are lodged in the hypostroma of the integument, and in con- 

 sequence the portions of integument to be mounted must, 

 when freed from the viscera and. musculature, be placed inside 

 upwards on the slide. 



My Synapta material, consisting of S. hispida and S. 

 digitata, was obtained from Naples, and I believe was 

 simply fixed and preserved in alcohol. I stained portions of 

 the body-wall by the safranin and lichtgriin method and 

 obtained good results. 



In many cases, especially of the older spicules of Amphiura, 

 it is difficult to decide upon the exact number of cells in con- 

 nection with a spicule, and such must be simply passed over. 

 The figures provided in the accompanying plate were all 

 drawn from spicules about which there existed no doubt 

 whatever as to the number of scleroblasts attached, and 

 these were only obtainable by careful and persistent 

 searching. 



The Origin of the Spicules in Amphiura elegans. 



In Cucumariidas (13) the plate-spicule originates as an 

 elongated granule (thick-set needle) with its length disposed 

 at right angles to the line joining the masses of the two 

 scleroblasts usually concerned in its deposition; in some 

 cases, however, four scleroblasts are concerned in the deposi- 

 tion, two being situated on each side of the needle. In 

 Amphiura elegans, on the other hand, the plate-spicule 

 originates in the same manner as the small superficial spicules 

 of the Cucumariidse do, viz. as an approximately spherical 

 granule contained within a single cell (fig. 2). This differ- 

 ence of origin between the holothurian and the ophiuroid 

 large plate-spicules can be correlated with other more general 

 differences affecting the manner of lime secretion as it occurs 

 in the two groups, and these I shall shortly indicate. For 

 the present it suffices to point out that the needle and the 

 granule correspond in form in both cases with the general 



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