ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 61 



taperino^ process like the " leader " of a growinsr fir-tree, with a single 

 or double circlet of small spines at the base. The median whorl is a 

 little farther from the apical whorl than in L. hocagei, being approxi- 

 mately midway between the apical whorl and the manubrium. The length 

 •of the fully-grown spicule is about 0'126 mm. 



The spicules are well adapted to protect the surface against parasites 

 and other enemies. They are arranged in a dense forest, with their 

 manubria firmly implanted in the cortex. They are developed, however, 

 in the interior of the body, far removed from their final position. 



A siliceous spicule contains an axial thread or " protorhabd," out- 

 side which is the coating of hydrated silica or opal. Very slender 

 protorhabds were found, which were at any rate near the initial stage. 

 The protorhabd is responsible for the spicule's growth iii length, and 

 may continue its activities independently of any possible mother-cell. 

 With the protorhabds minute formative cells were found associated ; 

 they are probably responsible for the arrangement of the silica around 

 the protorhabd foundation. There are also larger accessory cells, 

 probably silicoblasts, which supply the formative cells with the necessary 

 material. 



The author describes the devefopment of the discorhabds, and 

 advances the theory that the position of the whorls corresponds with 

 the nodes in a vibrating rod, the vibration being due to the stream 

 of water through the canal system. The coincidence of the positions 

 of the median and subsidiary whorls with those of the rings of 

 formative cells is noted. It may be that the formative cells have a 

 sort of tropism ; that they are sensitive to vibrations in such a way 

 that they are induced to avoid the internodes and take up their positions 

 at the points of comparative rest of the vibrating rod, with which they 

 are doubtless at first in immediate contact. The diflference in the 

 position of the median whorl in the two species can be mechanically 

 accounted for. It is unlikely that natural selection has had to do with 

 the differences in the apices of the spicules in the two species. The 

 facts support the view that the characters separating species are usually 

 of little or no importance to their possessor in the struggle for existence, 

 while adaptations are usually shared by many different species. 



Irish Sponges.* — Jane Stephens reports on the sponges collected by 

 the dredging expeditions of the Royal Irish Academy and the Royal 

 Dublin Society. The number of species is thirty-eight, including two 

 species new to science — MycaU (Faresperella) atlantica and Forcepia 

 fragilis. The first is especially interesting, because it is the first repre- 

 sentative of the sub-genus Paresperella found in the Atlantic Ocean. The 

 following five species are noted for the first time within the Irish area : — 

 Laxosuberites ectyoninus Topsent, Desmacidoyi fruiicosum (Montagu), 

 Hymenancoraconjungens Lundbeck, 3Iicrociona Isevis Bowerbank, Tragosia 

 polypoides Schmidt. The first and third have not been taken previously 

 off any part of the British Isles ; each, in fact, has only been recorded 

 once before— the former in the Mediterranean, the latter off the south 

 coast of Iceland. A plate of spicules is given. 



* ProC. B. Irish Acad,, xxxiv. (1917) pp. 1-16 (1 pi.). 



