38 W. WOODLAND. 



I may also mention that the dark granules, so conspicuous 

 in the scleroblasts of manj^ CucumariidaB, are also present in 

 the scleroblasts of Antedon ; indeed, they are usually dark 

 without any additional staining with lichtgriin. 



The Small Plate-Spicules of Synapta hispida and 

 s. digitata, 



In addition to the plate-and-anchor spicules of S. 

 inhaerens I have examined the similar (though easily 

 distinguishable) spicules of S. hispida and S. digitata, 

 and, as might have been expected, I find that the disposition 

 of the scleroplasm concerned in their formation is essentially 

 the same as that which I described in Study IV. Through 

 lack of material I have not as yet been able to ascertain the 

 disposition of the scleroplasm in the early stages of develop- 

 ment, though I hope to do so shortly. 



Besides these conspicuous plate-and-anchor spicules there 

 exist in S. hispida and S. digitata (though not in S. 

 inhaerens) small elongate plate-spicules, containing in the 

 former species a single perforation in their centre, and the 

 development of these perforate plates of S. hispida is 

 remarkable. I may mention that these small plates are 

 particularly numerous in the region of the rauscle-bands, 

 though they are also to be found in the intervening spaces. 



The plate in both species arises quite normally as a more 

 or less spherical granule in the centre of a single scleroblast 

 (fig. 23), and, as in Antedon, this gradually becomes elon- 

 gated (fig. 24) and plate-like, but, differing from Antedon, 

 the nucleus of the scleroblast remains single throughout the 

 entire development. In S. digitata these plate-spicules 

 cease growth at the stage depicted in fig. 30, which, it will 

 be noticed, is identical with the stage of development repre- 

 sented by fig. 24 of the plate-spicule of S. hispida. In this 

 latter species the plate elongates considerably, and expands 

 laterally to some extent except in the vicinity of the nucleus, 



