Afiscellatieous. 493 



in a very elegant manner in the form of a double comb, possess very- 

 strong outlines in a great part of the retina. The retina of the 

 Plagiostoma also, both Sharks and Rays, contains fibres of a breadth 

 of as much as OOl mill., which exhibit all the characters of the 

 varicose fibres with double outlines which occur in the nervous centres. 

 Lastly, I have observed that in the eyes of many Dogs, the optic 

 nerve is still white at its entrance into the eye, and that it is only in 

 the retina that the nervous fil)res become pale and transparent. But 

 the change takes place very soon after the entrance of the optic nerve, 

 whilst in the fishes just mentioned, the fibres with double outlines 

 extend over a great part of the retina, and only pass by degrees 

 to the aspect of the ])ale fibres. In a physiological point of 

 view it is remarkable that in the Fishes of which I am speaking, 

 notwithstanding the double outlines of the nervous fibres, the retina 

 appears to be tolerably transparent during life, whilst in the Rabbits 

 and Dogs it is opaque and white, in the whole extent of the fibres 

 with double outlines. In the former case the influence upon the 

 sight does not appear to be important, but in the latter the perception 

 of light must be hindered or disturbed as far as this peculiarity of" 

 the fibres extends : and the ophthalmoscopic effect of the bottom of 

 the eye, and especially of the entrance of the optic nerve, must present 

 remarkable modifications in all the animals in which a state similar 

 to that which has long been known in the Rabbit exists. — Comptes 

 Rendus, Oct. 20, 185G, p. 743. 



Remarks on Nika edulis, Risso. By William Thompson. 



The possession of a healthy specimen of XiAa edulis has enabled 

 me to offer the following remarks, which, I trust, may add some- 

 thing new to what is already known of this species. 



The first specimen I obtained by dredging on the 2nd July, 18.53. 

 I find by my notes, which were made at the time, that it was a 

 female, and in spawn ; the ova were darkish green, the animal itself 

 was of a cream colour, and spotted with red dots ; the spots were 

 of different sizes, perfectly roimd, and rather thickly and regularly 

 placed. This specimen was dead before I examined it, and this will 

 account for the difference of colour as contrasted with the specimen, 

 the more immediate subject of the present paper. I had previously 

 obtained one specimen, and a third s{)ecimen, also in sjiawn, was 

 brought to me on the 20th July, IS.'io ; the ova were bright green, 

 and the animal of a cream colour. This specimen was dead when 

 examined. 



The subject of the present paper was brought to me alive by my 

 dredger on the 21st February in this year, and lived three weeks. 

 It was dredged in Weymouth Bay, near the mouth of the harbour. 

 The colour in this living specimen was very different from that of 

 the dead specimens I had previously obtained. When first brought to 

 me, the whole animal was a light greenish-drab, irregularly and thinly 

 sprinkled with pure white stars ; the carapace and covering of the 

 abdomen were aUke transparent, and the intestines could be easily 



