TRANSACTIONS OF THE SECTIONS. 101 



Comis, Ttirritella, species or specimens are found with the earlier part of the spire 

 partitioned off. The same phenomena of varices is seen in many bivalves ; and a 

 process of shutting off cells in the lower valve is characteristic of several oysters." 

 These structures were then shown to result from the periodic enlargement of the 

 generative organs. " On examining a Nautilus-sh.e\\, two large muscles are seen 

 to have been placed in the lower part of the body-chamber, and connected round 

 the involute spire by a narrower muscle — an arrangement to which the shell may 

 owe its involute form. Beneath the muscles are the liver, which overlaps the 

 spire, the ovaries, which abut on a large part of the septum, and certain digestive 

 organs above these. Before any new chamber can be made, the shell-muscles 

 must have moved forward ; and before any increase in the ovaries can take place, 

 a space must be formed behind. As the animal steadily grows, all its organs 

 woidd enlarge; and, with each successive brood, the distended ovaries would 

 require more space. There is a similar gradual increase in the size of the air- 

 chambers. And, since the development of ova woidd necessitate a forward-growth 

 of the mollusk, the discharge of the ovaries would leave an empty space behind, 

 into which the creatm-e coidd not retire, which would then be shut off" by a 

 septum moidded on the animal's body. The Argonaut similarly accumtdates its 

 eggs in the involute part of the shell, but, not being attached to it, does not form 

 septa. In the male Nautilus the testes are placed in exactly the same position as 

 the ovaries of the female, and, excepting the liver, form the largest organ in the 

 body. It may therefore be concluded that the development of the male org^ans 

 would produce results similar to those in the other sex, and likewise end in the 

 formation of chambers. There are no other organs of the body which are liable to 

 periodic changes in size ; and therefore, as the position and progressive enlarge- 

 ment with age of the generative apparatus necessitate results like those seen in 

 the chambei's and septa, I regard one as the catise of the other." The author then 

 applied his theory to the Dibranchiata. Connecting the chambers is the tube 

 known as the siphimcle, ninning through every septum to the first, but not 

 through the nidimental capsule. Seeing the extreme elasticity of many mem- 

 branes of invertebrata — as, for instance, the oral membrane of a starfish — the 

 author pointed out that, when ova were discharged by the Nautilus, there must 

 remain the empty membrane, which, being attached to the base, could not but 

 contract into a tube, smaller or larger, according to its tenuity or vascularity. 

 The fine siphuncle of the Nautilus would indicate a single highly contractile 

 membrane ; the large siphuncle of Actinoceras may indicate two or three mem- 

 branes contracting difl'erently. 



Mr. R. F. Wbight exhibited some Trap-door Spiders from Corfu. 



Dr. E. Perceval Wright exhibited Professor T. Huxley's and Mr. Hawkins's 

 * Comparative Osteology.' 



Phtsioiogt. 



Address hy Dr. Edwaed Smith, LL.B., F.B.S., President of the Suhsecfion. 

 It has been customary for the President of this Subsection, on taking the chair, 

 to deliver an address, less pretentious and of a less general nature, perhaps, than 

 he wovdd have considered it his duty to prepare for the General Section, but always 

 offering observations on the progress of the science, whether in its entire aspect, or 

 in some points of view which woidd be the most interesting to his audience ; and 

 a custom so valuable and time-honoured must not, even in less able hands, be per- 

 mitted to lapse. I purpose, therefore, to open the Meetings of this Department with 

 some introductory observations ; and taking the special rather than the general plan 

 of procedm'e, I shall confine my observations to a question limited in its range of 

 knowledge, but scarcely limited in its importance and imiversal interest — to a 

 statement of the present condition of the dietary question, considered, first, in its 



