346 SUMilAEY OF CURRENT RESEARCHES RELATING TO 



the view they have taken ; for, as the result of his own observations, 

 he finds that when young the tube is hollow, but when old the cavity 

 becomes jilled up with a mucous substance. 



Ecliinodennata. 



Structiire of Pedicellariae.* — A. Foettinger has examined the 

 gemmiform pedicellarias of SphcBrecldnus granularis. He finds that 

 the three more or less ovoid glandular sacs which are formed on 

 the stalks of these, are surrounded by the common epithelial mem- 

 brane which invests the whole of the organ. They open to the 

 exterior by an orifice at their superior extremity, and they alternate 

 in position with the valves which form the head of the pedicellaria. 



After decalcification by means of chromic acid, and staining with 

 carmine, the following tissues can be seen on making a transverse 

 section of a pedicellaria at the level of these glands ; there is an 

 external epithelium, containing a large number of pigment-corpuscles, 

 a layer of connective fibrillse which separates and unites the glan- 

 dular sacs ; these have an external layer of flattened muscular fibres, 

 with an oval nucleus, and these fibres are arranged concentrically 

 around the orifice of the gland ; the contents of the sac vary greatly, 

 being in some cases formed of a granular, and probably mucous, 

 matter which contains refractive corpuscles which swell up under the 

 action of water, and are, doubtless, modified nuclei ; in other cases 

 the substance is filamentous, but this is ascribed to the coagulating 

 action of alcohol ; this substance swells up considerably on contact 

 with water, &c. ; and this increase in volume, when it happens with an 

 uninjured pedicellaria, must lead to the outpouring of the contained 

 mucus. When certain transverse sections are made, the contents of 

 the sac are seen to be constituted almost solely of protoplasm with 

 nuclei and cell- walls more or less intact. In longitudinal sections 

 some of the glands present a protoplasmic layer investing the base 

 and the walls. The author would explain these facts by considering 

 that the glandular sacs are primitively filled by a tissue formed of 

 polyhedral cells, and making a compact mass. At a certain time 

 these cells are converted into mucus, and this change goes on until 

 all the external cells are aftected by it. 



The three valves which form the head of the gemmiform pedi- 

 cellaria are pyriform in profile view, and ovoid from in front; the enve- 

 loping layer is merely epithelium ; below it there is a layer of granular 

 and fibrillar connective tissue, which is generally very delicate, but is 

 abundant between the valves, and near their upper surface. Beneath 

 this tissue we find a glandular sac, which is double above ; at the peri- 

 pheral extremity the two branches unite into a single canal. This 

 glandular sac would also seem to have its primitive contents formed 

 of a compact celltdar tissue. Echinus melo and EcTiinometra subangu- 

 laris have at the base of the head of their pedicellariae organs which 

 are very probably homologous with those found on the stalk of S. 

 granularis. M. Foettinger has also examined the pedicellariae of 



* Arch, de Biol., ii. (1881) pp. 455-96 (3 pis.). Bull. Acad. R. Belg., ii. (1881) 

 pp. 493-504. 



