736 EEPORX — 1887. 



'J'hese tliree plates soou fuse together and with the top stem joint, and they thus 

 form the angles of the large plate, hitherto mistaken for a simple centrodorsal. 



From a comparison of the development of antedon with that of other Echino- 

 derms it seems almost certain that, as Barrois has suggested, the stalk represents the 

 prseoral lohe. 



11. On the True Nature and Function of the Madreporic System in Ecltino- 

 dermata. By Dr. M. Hartog. 



This, always regarded hitherto as an apparatus for taking up sea-water, is now 

 shown to be excretory ; for the following reasons : — 



1 . Physiulo(/ieal. — An animal with a central cavity, or series of cavities, con- 

 taining dissolved in their liquid substances of osmotic attraction, must tend to 

 turgesce like a vegetable cell, and hence require some apparatus to eliminate the 

 excess of liquid. This is provided by the nephridial system with its ciliated 

 nephrostomes in most animals. The only organ that can have this function in 

 echinodermata is the madreporic canal and plate. 



2. Morpholoyical. — The madreporic system, on togenetically formed of an endo- 

 thelial sac opening through an epilelastic invagination, is equivalent to an Annelid 

 nephridium. 



3. Comparative. — In most Holothurians the respiratory trees are sufficient to 

 expel the excess of water, and the madreporites have lost direct connection with 

 the outside ; in the Elasipoda, where the trees are absent, the madreporite opens on 

 the surface. 



4. Demonsf ratios. — In Echinus sphara the ciliary current in the madreporic 

 canal is seen to carry suspended bodies towards tlie plate, and this is the true test 

 of the direction of ciliary currents. 



To meet the objection as to how enough liquid was supplied for a general 

 erection of the tube feet, I would suggest that a sliglit dilatation of the cavity of 

 the gut, freely taking up sea-water, would compensate for the withdrawal of liquid 

 from the ampulla?. 



FRIDAY, SEPTE3IBER 2. 



The following Papers were read : — 



1. Discussion in conjunction with Section C on the 'Arrangement of 

 Museums.' 



2. On the Vascular System and Colour of Arthropods and Molluscs 

 By Professor Lankester. 



3. Notes on the Genus Phymosoma. By W. F. R. Weldon. 



4. On the Degeneration of the Olfactry Organ of certain Fishes. 

 By Professor WiEDERi5HEiM.' 



It has been shown by Johannes Miiller tha t an olfactory organ similar to that 

 of other fishes is wanting in many species of tlie genus Tefrodon, but that in its 

 place there is on either side of the head a solid tentacle-like process of the skin, 

 into which the olfactory nerve extends. This is all that unfil now was known on 

 the subject. 



Having, however, recently looked into the matter, I am able to give the following 

 short account of my results. 



' Published in the Festschrift zu Koelliker's 'Otvn Geburtstag. Leipzig, 1887. 



