510 ACCESSORY EYES IN THE VERTEBRATA. 



they may be used in the perception of light. The most important of such 

 organs are those found in Chauliodus, Stomias, etc., the significance of which 

 was first pointed out by Leuckart, while the details of their structure have 

 been recently worked out by Leydig 1 and Ussow. They are distributed not 

 only in the skin, but are also present in the mouth and respiratory cavity, a 

 fact which appears to indicate that their main function must be something 

 else than the perception of light. It has been suggested that they have the 

 function of producing phosphorescence. 



Another organ, probably of the same nature, is found on the head of 

 Scopelus. 



The organs in Chauliodus are spherical or nearly spherical bodies 

 invested in a special tunic. The larger of them, which alone can have any 

 relation to vision, are covered with pigment except on their outer surface. 

 The interior is filled with two masses, named by Leuckart the lens and 

 vitreous humour. According to Leydig each of them is cellular and receives 

 a nerve, the ultimate destination of which has not however been made out. 

 According to Ussow the anterior mass is structureless, but serves to support 

 a lens, placed in the centre of the eye, and formed of a series of crystalline 

 cones prolonged into fibres, which in the posterior part of the eye diverge 

 and terminate by uniting with the processes of multipolar cells, placed near 

 the pigmented sheath. These cells, together with the fibres of the crystalline 

 cones which pass to them, are held by Ussow to constitute a retina. 



Eye of the Mollusca. 



(362) N. Bobretzky. " Observations on the development of the Cephalopoda " 

 (Russian). Nachrichten d. kaiserlichen Gesell.d. Freundcder Natunviss. Anthropolog. 

 Ethnogr. bei d. Universitiit Moskau. 



(363) H. Grenacher. " Zur Entwicklungsgeschichte d. Cephalopoden." Zeit. 

 f. wiss. Zool., Bd. xxiv. 1874. 



(364) V. Hensen. " Ueber d. Auge einiger Cephalopoden." Zeit. f. wiss. 

 Zool., Vol. xv. 1865. 



(365) E. R. Lankester. " Observations on the development of the Cephalo- 

 poda." Quart, y. of Micr. Science, Vol. xv. 1875. 



(366) C. Semper. Ueber Sehorgane von Typus d. Wirbelthieratigen. Wiesbaden, 

 1877- 



Eye of the Arthropoda. 



(367) N. Bobretzky. Development of Astacus and Palaemon. Kiew, 1873. 



(368) A. Dohrn. " Untersuchungen lib. Bau u. Entwicklung d. Arthropoden. 

 Palinurus nnd Scyllarus. " Zeit. f. wiss. Zool., Bd. xx. 1870, p. 264 et seq. 



1 F. Leydig. "Ueber Nebenaugen d. Chauliodus Sloani." Archiv f. Anal, 

 und Phys., 1879. M. Ussow. " Ueb. d. Bau d. augenahnlichen Flicken einiger 

 Knochenfische." Bui. d. la Soc. d. Naturalistes de Moscon, Vol. i.iv. 1879. Vide 

 for general description and further literature, Giinther, The Study of Fish>-s t Edinburgh, 

 1880. 



