80 SUMMARY OF CUBRENT RESEARCHES RELATING TO 



is due to haemoglobin ; differing slightly in the " albuminous portion 

 of the molecule " from that of vertebrates. 



Structure and Function of the Sphaeridia of Echinoids.* — Mr. H. 

 Ayers gives a careful description of these sensory organs, the dis- 

 covery of which we owe to Prof. Loven ; they may be spheroidal or 

 oviform in shape, but there is a typical form for each species ; in each 

 sphserid we may distinguish externally a base, which is composed of a 

 mamelon of the test, a joint, which forms the connection between the 

 base and the globule, and chiefly composed of muscle-cells and 

 fibrous tissue, and, lastly, a globule, or body of the sphaerid, which 

 consists of head and neck.'' The calcareous matter of the globule 

 is a hard, very brittle, vitreous carbonate of lime, deposited in more 

 or less concentric layers ; it is deposited or inclosed between organic 

 layers. The canal system is best studied after the slow removal of the 

 calcareous matter by dilute acid, and treatment with hard Canada 

 balsam, or by staining ; the reticulated tissue of Loven is then seen 

 to be a system of canals, which is but a modified form of the canali- 

 cular spaces of the spines ; within the canals are found nerve-cells, 

 and in some cases (e.g. Echinus melo) a chlorophyll-green fluid. 

 There is an epithelial covering, the cells of which are known to 

 have cilia only by the currents caused by their motion ; when 

 dead they may be seen to be not scattered over the entire surface of 

 the sphserid, but confined to patches of various size on the sides of 

 the neck and globule. The nerve-supply comes from the tentacular 

 nerve-trunk, and the cells form a network of filaments with here and 

 there irregular knots — the nucleated portions of the cells. The 

 ends of the filaments are club-shaped or pyramidal, with the larger 

 part directed outwards. 



Mr. Ayers points out that these organs are more highly specialized 

 than Loven's description would lead us to think, and they are much 

 more so than similar organs among the Medusae. As to their func- 

 tion it was observed that on the addition of a drop of dilute acetic 

 acid to the sea-water in which the urchin is living, there is a sudden 

 stimulation and increased activity of all the external organs, the 

 sphaeridia being the first to recognize the presence of the acid, and 

 giving one or two quick short jerks, followed by a swaying or rotat- 

 ing movement. They seem to have the function of perceiving 

 chemical changes in the surrounding water and reporting the same to 

 the nervous centres of the animal ; they do not seem to be affected in 

 the least' by sounds. 



Ambulacra of Diadematidse.f — Prof. P. M. Duncan describes the 

 anatomy of the ambulacra of recent Diadematidae, in the genera 

 Diadema, Echinoihrix, Centrostephanus, Astropyga, Micropyga, and 

 Aspidodiadema, The research is of classificatory importance. 



Star-fishes of the * Talisman.' | — Prof. E. Perrier states that fifty- 

 four species, represented by nearly two hundred examples, of star- 



* Quart. Journ. Micr. Sci., xxvi. (1885) pp. 39-52 (1 pi.). 

 t Journ. Linn. Soc. Lond., xix. (1885) pp. 95-114 (I pi.). 

 i Comptes Eendus, ci. pp. 884-7. 



