INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 961 



brane ; (2) a neuro-muscular layer ; (3) a tissue with numerous large 

 cells ; (4) a layer of large areolar spaces and gland-cells and ducts ; 

 (5) the central mass composed of a very finely reticulated substance, 

 densely filled up with mucous matter. 



As to the characters of the " head " of the P. glohifera ; a longi- 

 tudinal section reveals the presence of the following parts : — (1) a 

 fine investing membrane, composed of a few epithelial cells. (2) A 

 stratum containing a few nerve-cells. (3) The walls of a large 

 saccular body bounded by a moderately thick layer of horizontally 

 disposed muscular fibres. (4) A reticular tissue terminating in folli- 

 cular gland-cells, which form a layer internal to the wall of the sac, 

 and of some considerable tliickncss ; the glandular sac is divided into 

 two chambers. Nerve-centres with fibres for each valve communicate 

 with the strong muscles which hold together the valves of the pedi- 

 cellaria. On the inner surface of the expanded valves there are to be 

 found three oval-shaped cushions, which are finely papillate and are 

 richly provided with nerve-fibres. 



In regard to the suggested functions of these parts we find first 

 of all this notable discharge of mucus ; " when the tactile cushion of 

 the pedicellaria comes into contact with a tangible object of foreign 

 matter, the valves close and a discharge of mucus takes place " ; this 

 mucus surrounds the object and then the neighbouring spines gradu- 

 ally disentangle it, and the currents of water carry it off. The author 

 has made observations on Astropeden aurantiacus which strongly 

 confirm this view. 



Mr. Sladen then gives a short account of the structure of the same 

 kind of pedicellaria in Echinus melo, which seems to resemble the 

 younger forms found in S. granularis. The pedicellarife tridentes 

 appear to have the function, already noted by A. Agassiz, of removing 

 the pellets of f.ccal matter ; that of the P. triphyllce is probably to 

 seize smaller particles of foreign matter which escape the larger 

 pedicellarife. 



New Echinodermata.* — In addition to Hymenodiscus Agassizii, 

 referred to in the next note, M. E. Perrier jdescribes some very inter- 

 esting forms obtained during the dredging operations of Professor 

 A. Agassiz in the deeper parts of the Gulf of Mexico ; among these 

 are two new species of the genus Zoroaster of Wyvillc-Thomson 

 (Z. Slgshcii and Z. Acldeyi). 



Z. Sl'jsheii is at once distinguished by the considerable projection 

 made by the enormous ossicles of its disk, wliich is thus rendered 

 clearly distinct from the arms and comparatively voluminous. Tho 

 arms, which are nearly rigid, are conical, and their skeletim consists of 

 nine regular series of s(^uare ossicles. In Z. Acldvyi the ossicles of 

 tho disk are not salient, the disk is continuous with the arms, which 

 are about twelve times as long as its radius, so that the aninuil lias 

 the physiognomy of a Chataslcr. These arms are much more mobile 

 than those of the other 6i)ceies, and are formed of seventeen rows of 

 rather small ossicles. In the two species before tho author the plates 



* ' Comptea Rendus,' xci. (1880) p. 430. 



