54 SUMMARY OF CURRENT RESEARCHES RELATING TO 



to show that they are tactile organs. The smallest, such as the trifoliate 

 pedicellarias, have certainly the action of scavengers and cleaners ; the 

 larger, such as the tridactyles, serve principally to ward off larger living 

 bodies, and also to hold on to fixed foreign objects during locomotion. 

 The gemmaeform pedicellarise also have this function, and their seizing 

 power is aided by the secretion of the glandular sacs. 



The author next deals with tho globiferi of Centrosteplianus longi- 

 spinus, of which two kinds are described. Some are compressed, and have 

 an exceedingly short stalk, while others are more delicate, and have a 

 longer stalk. Each consists of three spheres, which are closely appressed 

 and fused at their points of contact. The glandular contents are of a 

 yellowish colour. In the centre of the stalk there is a calcareous rod, 

 which has generally a spherical termination, and above it the integument 

 forms a sort of hood. 



As to the minute structure of the globiferi, the author states that the 

 investing epithelium consists of cubical cells, among which are a large 

 number of yellow pigment cells. The interior of each oviform gland is 

 occupied by long cylindrical palisade-like cells, which have but a narrow 

 central space. If a living globifer be compressed, the cells may be seen 

 to suddenly pass out by the orifice of the glands. The cell may be shown 

 to have been broken off above the nucleus. The examination of sections 

 demonstrates that the glandular contents consist of a mucous mass, with 

 an investment of cells along the wall. The latter are surrounded by a 

 small quantity of protoplasm, and do not appear to have definite boun- 

 daries. Their nuclei are of some size, and nearly always contain some 

 distinct nucleoli. Among them there are scattered smaller cell-nuclei. 



The globiferi can be best made out in Splisercechinus granulans, where 

 they were first observed by the author.* The fact that these organs 

 have hitherto escaped defection is doubtless explicable by their super- 

 ficial resemblance to pedicellariaa, from which, indeed, they appear to 

 have been derived. 



The spines are next discussed, those of Dorocidaris papillata being 

 first described. All but the large thick spines present an arrangement 

 which has not yet been detected in any Urchin. At the base there is a 

 mass of large glandular cells. The thickening at the base is due to the 

 thickening of the connective substance and the superjacent epithelium. 

 The latter is made up of ordinary epithelial cells and of glandular cells. 

 The latter are tubular, and are surrounded by a membrane. The cell 

 itself consists of a granular, highly refractive mass, and a large number 

 of cilia project from its free ends. The epithelial cells are fine and fila- 

 mentar, and the base is connected with nerve-fibres. Nerve-trunks can 

 be made out in each spine, and these can be traced to the nearest ambu- 

 lacral nerve. In Sphser echinus granulans there is a basal nerve-ring, 

 whence nerve-fibres pass to the longitudinal muscular fibres, and the 

 capsule of connective substance. Above the ring the superficial epithe- 

 lium is much thickened, and the cylindrical cells, which are long and 

 hair-like, carry long cilia at their free ends. Below the epithelium is 

 the muscular layer, formed of longitudinal smooth fibres, which have 

 their origin in the upper calcareous piece of the spine, and are inserted 

 into the calcareous pieces of the body-wall at the base. 



The last kind described are the rotating dorsal spines of Centrosteplianus 



* See this Journal, 1886, p. 452. 



