57& 



NA TURE 



[Oct. 9, li 



In section it is seen to be composed of a series of concentric 

 lamellae. Its substance is continuous with the general calcare ms 

 substance of the tegmentum at its margins. The pear-shaped 

 cavity of the eye, formed by the shell-substance, is lined by a 

 dark brown pigmented choroid membrane of a stiff and appa- 

 rently somewhat chitinous texture. This membrane exactly fol- 

 lows the shape of the cavity, but, by projecting inwards beyond the 

 margin of the cornea all round, forms an iris of a less diameter 

 than the latter. A perfectly hyaline, strongly biconvex lens is 

 placed behind the iris aperture. It is composed of soft tissue, 

 and diss 'Ives in strong acetic acid. The optic nerve at some 

 distance from the retina is a compact strand, but before reaching 

 the latter has its numerous fine fibres separated and loose. The 

 retina is composed of a single layer of rather short but extremely 

 distinct nucleated rods of roughly hexagonal section, with their 

 free ends presented to the light. Immediately behind them is a 

 dense mass of nerve-fibre-, with numerous nuclei and nerve-cells 

 interspersed. The n-tina is on the type of that of Helix, and 

 not, as night have been supposed, on that of the dor-al eyes of 

 Oncidium. A large part of the peripheral fibres of the optic 

 nerve do not pass to the retina, but pass outside the eye-chamber 

 by a series of apertures in the choroid round the iris margin, and 

 end at the shell-surface in a zone of touch-organs encircling the 

 eye. The touch-organs are identical in structure with the 

 smaller touch-organs already described as appended to offsets of 

 the larger touch-organs all over the shell. In giving off nerves 

 to a series of such small organs, the eye thus corresponds exactly 

 in structure to these larger touch-organs, and its homogeny with 

 them is thereby clearly indicated. The arrangement of the eyes 

 varies much in the different genera. In Schisochiton incisus 

 the eyes are restricted to single rows traversing the lines sepa- 

 rating the lateral area from the area centralis, and corresponding 

 in portions with the incisure laterales and courses of the prin- 

 cipal nerves. There are six rows of eyes, with six marginal 

 slits on the anterior shell, and six on the posteri u, and a single 

 pair on each of the intermediate shells, twenty-four rows in 

 all, wdth an average of about fifteen eyes in each, or, in 

 all, 360 eyes. In Acanthopleura spiniger the eyes are 

 irregularly scattered around the bases of the tubercles with which 

 the surface of the tegmentum is covered, and are confined in 

 the specimens ex < mined to the region of the margins of the 

 shells adjoining the mantle. The surface of the older regions 

 of the tegmentum stms in this species especially liable to flake 

 off, carrying the eyes with it, and it will probably be found, 

 when series of examples of various ages are examined, that the 

 eye- are originally more widely extended over the shell surfaces. 

 In Corephkum aculentum the eyes are very small, with corneas 

 oval in outline, the long axis of the oval being directed vertically 

 to the shell margin. They are never placed on the tubercles 

 with rows of which the shell-surface is covered, but between the 

 bases of these. The two kinds of pores lodging the organs of 

 touch are arrange I in vertical parallel lines with great regularity, 

 the large pores occurring at intervals in the line- of smaller 

 pores. The eyes are pre ent in enormous numbers, the anterior 

 shell alone bearing more than 3000, and the entire eight sheds 

 more than 11,50 1. In Tonicia marmorala the eyes arearranged 

 in single straight radiating rows on the anterior and posterior 

 shells. On each lateral area of the intermediate shells there are 

 from two to four similar rows of eyes. In Ornithochiton the 

 eyes are disposed somewhat similarly. In the genus Chiton, 

 eyes appear to be entirely absent, though the touch-organs of 

 two sizes and corresponding pores are present. In Molpalia, 

 Mangina, Lorica, and Ischnochiton, I have as yet detected no 

 eyes. In Chitonellus there are no eyes, and the supply of touch- 

 organs is scanty and confined to the margins of the tegmenta. 

 The arrangement and structure of the eyes and organs of touch 

 will probably be of great value in the classification of the Chi- 

 t nidas, which has hitherto proved so difficult a problem. No 

 traces of any structures resembling the eyes and touch-organs of 

 the ChitonidEE can be detected in the shells of Pa'ella or allied 

 genera. The tegmentary part of the shells of this group ap- 

 pears to be something sui generis, entirely unrepresented in 

 other Mollusca. Its principal function seems to be to act as a 

 secure protection to a most extensive and complicated sensory 

 apparatus, which in the Chitonidac lakes the place of the 

 ordinary organs of vision and touch present in other Odonto- 

 phora, and fully accounts physiologically for the absence of these 

 latter in them. Dr. \V. B. Carpenter observed the perforate 

 structure of the tegmentum in Chiton, though he did not 

 examine the nature of the contained soft network. The late 



Dr. Gray, in his well-known paper on the structure of Chitons, 

 recognised the fact that the tegmentum in the Chitonida? is 

 something peculiar to the shells of this family. 



On a Method of Studying the Behaviour of the Genus of Septic 

 Organisms under Changes of Temperature, by Rev. Dr. Dal- 

 linger. — Description of a new apparatus invented for this purpose. 

 A Vegetable Organism which Separates Sulphur, by A. W. 

 Bennett. — Description of Beegiatoa alba, an organism found in 

 the effluent water from sewage-works, known as the "sewage- 

 fungus," which has the property of separating sulphur out of the 

 organic matter in the water, or in the salt used in precipitating 

 the sewage, in the form of minute sharply refringent globules. 



On Ike Coagulation of Blood, by Prof. H. N. Martin and W. 

 II. Howell.— The blood of the Slider Terrapin, a turtle easily 

 obtainable in Baltimore, had been used for a number of ex- 

 periments, the object of which was to determine whether the 

 views entertained by Hammarsten or by Schmidt were most 

 reliable. The general conclusions went to show that the views 

 1 if Hammarsten were more in accordance with the results of 

 these observers. 



Prof. Schafer asked if the authors had made any experiments 

 with reference to the addition of lecithin and white corpuscles 

 respectively to the blood plasma. 



Prof. Martin replied that no experiments had been made with 

 lecithin, but that he had found that the plasma did not clot 

 when entirely free from white corpuscles or a watery extract ol 

 them. 



On the Blood of Limulus polyphemus, by Francis Gotch and 

 J. P. Laws. — The paper was chiefly interesting, as Prof. Schafer 

 remarked, on account of its indicating the combination of copper 

 with a proteid replacing the usual iron. 



On l r aso-motor Nerves, by Prof. H. P. Bowditch. — He gave an 

 account of some experiments he had been making to determine 

 the need of vaso-motor nerves. He had employed an entirely 

 new method, namely, the use of the plethysmograph. 



Demonstration of the Co-ordinating Centres of Kroneckcr, by 

 Prof. T. YV. Mills.— This subject had been previously practically 

 demonstrated to most of the physiologists present. The view, 

 in brief, held by Prof. Kronecker is that there is constituted in 

 the ventricle of the dog's heart a centre which, when injured, is 

 paralysed, and whose function of co-ordinating the muscular 

 movements to form a beat is thus lost, the heart going into what 

 is known as fibrillar contraction, which is wholly insufficient to 

 propel the blood through the body. 



Dr. Martin had seen this phenomenon when working on the 

 coronary artery, and thought it due rather to injury of the 

 nerves. 



Prof. Schafer held a somewdiat similar view. 

 Dr. Bowditch asked if, as the injuries referred to were 

 mostly superficial, they did not differ very much from the case 

 in point, which was a deep injury. 



Prof. McKendrick thought that if it was merely an injury of 

 a nerve that caused the phenomenon, the heart might be brought 

 back to its natural action ; while the fact was a dog's heart, he 

 understood, had never been recovered. 



. Dr. Mills also stated that Prof. Kronecker would, in conse- 

 quence of injury of this centre, explain deaths from slight pricks 

 of the heart, sudden death in heart disease in certain cases, and 

 death from chloroform. 



Prof. Schafer thought that from the evidences it was clear 

 electric excitation should not be used to recover hearts suffering 

 from chloroform administration, inasmuch as the phenomenon 

 could itself be caused by the application of an electric current. 

 Dr. Osier thought the strength of current usually used by 

 physicians in such cases was not so strong as those Prof. Schafer 

 jiad in view. 



On the Cardiac Nerv s of the Turtle, by Profs. Kronecker 

 and Mills. — This communication went to show that in the sea 

 turtle there were nerves whose function was perfectly analogous 

 to that of the vagi and accelerantes in mammals. The couise of 

 these nerves varied a good deal in different species and in 

 different individuals. It had also been discovered that the 

 pulsating great veins of the land turtle were under the influence 

 of the vagus. 



Prof. Martin had found in the Slider Terrapin a ganglion, 

 apparently answering to the thoracic ganglion of the dog, from 

 which the accelerator nerve passed to the heart. 



On the Functions of the Marginal Com olution, by V. Horsley 

 and Prof. Schafer. — The object of their experiments was to ascer- 

 tain the effect of stimulation of localised areas of the marginal 



