246 



NA TURE 



{jMLy 14, 1887 



ter, species of Dentalium Noe, and specimens of Sirpula, also a 

 large shark's tooth belonging to the genus Carcharodon. 



During the autumn of 1885 I visited Zante in the Austrian 

 Lloyd's steamer from Trieste to Athens. As the steamer only 

 anchored for a few hours, I had time only for a walk to the top 

 of the hill overlooking the town. A chain of hills trending 

 nearly north and south forms the backbone of the Island of 

 Zante. At the latitude of the town of Zante this chain is 

 broken by a strip of alluvial plain about 2 miles wide, stretch- 

 ing from the eastern to the western coast of the island. The 

 Castle hill is a mass of Pliocene marl, rising about 300 feet 

 above this plain at its eastern edge. The steep side of the hill 

 is channeled with innumerable ravines and gullies, and of the 

 same colour as the Pliocene beds of Lattakia. In coming down 

 the hill, I observed in one locality, within a radius of 30 feet, 

 the following species : — ■ 



Cerithium vulgatum, Brug. 

 Murex conglobatus. 

 Cardium edule, L. 

 Venus [Cytheraa) casina, L. 

 Ostrea, sp. 



All of these were more or less embedded, or had been 

 worked out by the rain, and lay at the bottom or sides of the 

 gullies. 



London, June 23. George E. Post. 



The Perception of Colour. 



I HAVE not yet heard it stated that our perception of colour 

 is slower for the blue and violet rays than for the green, yellow, 

 and red ones ; and as I think that this subject has interest for 

 many of your readers, they will perhaps carry out the following 

 simple experiments on themselves and their friends. 



A luminous object, such as a distant gas-lamp, an electric 

 light, or the moon, is looked at through a direct-vision prism 

 after it has been removed out of its case. The spectrum is of 

 course a bad one, but brilliant. Now, if the prism is rolled 

 backwards and forwards between the fingers, so that the spec- 

 trum oscillates through a small angle, it appears to bend like a 

 riding-whip which is being flicked from side to side. The blue 

 and Violet parts of the spectrum always lag behind. In fact, 

 as far as I could see, the spectrum, instead of being straight, 

 seemed to be gently curved, but very sharply bent between the 

 indigo and the violet part, which would show that the more 

 refractive rays are seen by us very much later (even proportion- 

 ately) than the others. 



As everybody is not able to detect this bending of the spec- 

 trum, the following experiment should also be carried out. In- 

 stead of rolling the prism, it is passed between the eye and the 

 object as quickly as possible, so that the spectrum is only seen 

 for an instant ; and it will be distinctly noticed that it seems to 

 flash from the red end towards the violet — a sure sign that the 

 red is seen first and the violet last. C. E. Stromeyer. 



Strawberry Hill, July 5. 



Breeding for Intelligence in Animals. 



Seeing the results that have been attained by breeding for 

 special qualities in dogs, why should not systematic efforts be 

 made to breed for general intelligence? The correspondents 

 who have from time to time furnished you with illustrations of 

 canine sagacity must be sufficiently numerous to form an Asso- 

 ciation to promote the interbreeding of intelligent dogs, and the 

 distribution of their oftspring to those who would foster and 

 cultivate their intellect. H. Rayner. 



June 27. 



The Nephridia oi Lanice conchilega. 



Since my paper on the nephridia of Lattice conchilega, 

 Malmgren, appeared in Nature (June 16, p. 162), I have 

 learned that the chief peculiarity to which I called attention in 

 my description of the nephridial system had been observed and 

 mentioned before. In the monograph on the Polycladen by Dr. 

 Arnold Lang, published in 1884, and forming one of the series 

 " Fauna und Flora des Golfes von Neapel," p. 677, occurs the 

 sentence : " Bei Lattice conchilega, Pallas, hat neuerdings Ed. 

 Meyer bei erwachsenen Thieren jederseits einen Langscanal 

 aufgefunden, welcher alle Segmentalorgane mit einander ver- 

 bindet, und nur an einer Stelle durch ein Dissepiment unter- 



brochen ist." Dr. Ed. Meyer has c\lled my attention to this 

 passage, and informed me that Dr. Lang received permission 

 from him to make use of this and other observations which he 

 ( Dr. Meyer) had made in the course of his studies on Cha;topoda. 

 The sentence quoted has been also cited by Dr. R. S. Bergh in 

 an article on "Die Excretionsorgane der Wiirmer," in Kostnos, 

 1885, Bd. ii. p. 115. That sentence is the only account yet 

 published concerning Dr. Meyer's observations on the nephridia 

 of the species in question. When my paper was printed I was 

 unaware of the existence of the sentence in Dr. Lang's mono- 

 graph, or of the reference to it made by Dr. Bergh. Unfortun- 

 ately I had not had time to read the monog aph through, and 

 had not suspected that there was in it a mention of a novel fact 

 concerning the anatomy of Chaetopoda. My examination ot 

 Lanice conchilega was made in entire ignorance that Dr. Meyey 

 had already investigated its anatomy ; otherwise I should of 

 course have mentioned his name in the summary I gave of 

 previous wor'.c on the subject. J. T. Cunningham. 



Edinburgh, June 30. 



THE PARIETAL EYE IN FISHES. 



THE discovery of the parietal eye in lizards by de 

 Graaf and Spencer is so recent that it is hardly 

 necessary to preface an account of the structure of that 

 organ in another group with the history of their 

 researches. 



Its high development in some lizards, and, so far as we 

 know, its rudimentary nature in all other existing groups 

 of vertebrates, including fishes and Amphibia, and lastly 

 its entire absence in Amphioxus, are, for those who see 

 in the latter the " Urvater " of the Chordata, points which 

 made it difficult to form any satisfactory morphological 

 conception of its origin. 



True, something that admitted of comparison with it 

 could be found in larval Ascidians ; and Spencer, at the 

 end of his able paper, endeavoured to trace its " rise and 

 fall" from its supposed homologue, the larval Tunicate 

 eye. 



With Wiedersheim and Carriere, I consider that Spencer 

 has placed the eye of the larval Tunicate at the wrong 

 end of the series — if it should come in at all ; for, as 

 experience has abundantly shown, it is very easy to com- 

 pare organs of the higher vertebrates with what are sup- 

 posed to be homologous organs in Amphioxus and the 

 Tunicata, and at the same time to be entirely in error. 

 I need hardly refer the reader to the instances in which 

 such comparisons have b3en shown by Dohrn in his 

 famous " Studien " to have been entirely wrong ; and 

 holding with him that Amphioxus and the Tunicata are 

 very degenerate vertebrates, and that from them but little 

 can be got for the elucidation of the problems of verte- 

 brate morphology, I felt the necessity of looking else- 

 where for the solution of that of the parietal eye in its 

 relations to the paired eyes. 



With these problems in view I began to study the 

 development of the pineal eye, and also its structure in 

 such fishes as might be expected to retain it in a more 

 developed condition than most of those we know. 



At Prof. Wiedersheim's suggestion I examined the 

 structure of the " pineal gland " in Ammocoetes of Petro- 

 tnyzon planerl, in the hope that something more might 

 come out beyond that which the able work of Ahlborn 

 has already made known to us. The result was, in a 

 sense, disappointing, but not unexpected, for, remember- 

 ing Dohrn's researches, and bearing in mind that the 

 paired eyes of Petromyzon are rudimentary in Ammocoetes, 

 first becoming capable of vision in the adult, I had firm 

 hope of good results from the examination of sexually 

 mature animals. 



In the adult the discoveries made exceeded my expecta- 

 tions ; and after examining this animal I proceeded to make 

 sections through the brain of Myxine. Here, again, the 

 finds were important, and the research was extended to 

 specimens of Bdellostonia and Petromyzoii tnarinus, 



