322 



Mr. R. J. Lee on the 



[Apr. 28, 



I. " On the Organs of Vision in the Common Mole." By Robert 

 James Lee. Communicated by Samuel Solly, F.R.S. Re- 

 ceived March 30, 1870. 



The eye of the Common Mole and the structures connected with it un- 

 dergo some remarkable changes during the growth of the animal. The 

 gentleman who does me the honour to present the results of an investiga- 

 tion into that subject to the Royal Society was desirous that it should be 

 undertaken in order to ascertain the cause of the anomalous condition in 

 which the organ of vision is found in the adult Mole. 



It was the suggestion of Mr. Solly that an examination of the eye of the 

 young or foetal Mole might assist in the explanation ; for Mr. Solly had re- 

 flected much on the subject, and entertained reasons for believing that such 

 an inquiry would be attended with a satisfactory result. 



It is known that there is distinct evidence of the existence of an eye 

 and other parts concerned in the endowment of sight in many of the various 

 species of the Mole genus. To what extent, however, the defective state of 

 the organs permit of sight, or whether the animal is totally blind, are 

 questions still undecided. 



That the organs of vision in the young Mole would be found in a more 

 perfect state than in mature age was what Mr. Solly anticipated, while he 

 conjectured, for physiological reasons, that the cause of the difference 

 between them would be found to be a process of atrophy or degeneration in 

 the various structures essential for the enjoyment of sight. 



The specimens sent me for the purpose of examination consisted of a 

 female Mole, which appeared from its dimensions to have attained the full 

 period of development, if it had not somewhat exceeded it, and of six unborn 

 young about an inch and a quarter long, and, as far as I could judge, 

 beyond the middle of the period of gestation. 



Before entering into anatomical details, I venture to review briefly the 

 researches which have been made by anatomists into this subject. A 

 summary of the views entertained by those who preceded him is given by 

 Gottfried Treviranus, in his work published in 1820, ' Yermischte Schriften 

 Anatomischen und Physiologischen Inhalts,' in the chapter on the Nerves 

 of Sense in Mammalian Animals. From this account it appears that it was 

 Zinn who first described an optic nerve in the Mole, and declared it to be 

 a branch of that division of the fifth pair of nerves which is distributed to 

 the nose. 



The description by Zinn was published in the fourth volume of the 

 Commentaries of the Royal Society of Gottingen. " The optic nerve," 

 he says, " is long and of considerable tenuity. Its origin is the same as 

 that of the very large nerve which passes to the proboscis. It takes a 

 long oblique course, lying above the muscles of the nose, and passing in an 

 outward and backward direction, surrounded by dense structures, is finally 



