KEVIKW. 291 



exposure of green surface to the solar rays. On the other hand if, 

 as is the case according to received theories, the process which goes 

 on in the retina is not important as an absorption or (to use a 

 better term) a conversion of energy quantitatively, but only quali- 

 tatively, that is to say, in respect of initiating active changes in 

 the nerve-end cells with the subsequent consequences of which the 

 amount of energy converted has not so much to do as has its quality, 

 then we can understand that a lens which disposes the solar rays on 

 the retinal surface in a manner conducive to the localisation of their 

 differing quality, has importance and value. 



11. A melancholy instance of the extent to which Dr. Patten acts 

 upon the principle of bending facts to theory, even at the risk of 

 the grossest disrespect to contemporary authors of acknowledged 

 competency, is found in his treatment of Sars's observations on the 

 luminous organs of Euphausia. Patten wishes to consider these 

 organs as eyes, and instances of his hypothetical " heliophags ;" 

 accordingly he suggests that Sai's was misled by flashings of reflected 

 light when he stated that they gave out light at intervals. In a 

 note at the end of Patten's paper the editor of the ' Mittheil- 

 ungen ' very honestly states that Messrs. Paul M lyer and Giesbrecht 

 have in consequence examined three living specimens of Euphausia, 

 and entirely confirm Sars's observations and refute the unjust 

 insinuations made by Dr. Patten. 



12. A similar unwarrantable adhesion to theory, in the face of 

 opposing facts, is seen in Dr. Patten's attempt to evade the conse- 

 quences of the observations of Lankesterand Bourne on the lateral 

 eyes of Scorpions and Limulus, in regard to the latter of which 

 animals they have the confirmatory evidence of Grrenacher. Dr. 

 Patten has propounded a theory of the Arthropod eye, to the effect 

 that it is in all cases derived from a vesicle formed by invagi- 

 nation of the epidermis, and consists, therefore, of three layers of 

 cells, viz. the two layers of the flattened vesicle and the epidermic 

 layer which grows in front of it during its nipping off and detach- 

 ment from the point of invagination. It is probably true that this 

 is the structure and the ancestral history of the ordinary compound 

 eyes of Crustacea and Insects : but there is no justification in the 

 small area of facts observed by Dr. Patten himself for including 

 all Arthropod eyes, all ocelli wherever situated and however 

 constructed under this type. It is not clear why Dr. Patten 

 insists on the universality of his generalisation, applying it to 

 groups of Arthropods winch he kuoww nothing about, and pre- 

 suming to deny the accuracy of observations which he has not 

 taken the trouble to test. Lankester and Bourne described the 

 ommateum of the lateral eyes of Scorpions as being " mono- 

 stichous," like the great lateral eyes of Limulus. They figured sec- 

 tions of the lateral eyes of both Buscorpius italicus and of 

 Androctonus funestus. Their sections are in existence, and 

 leave not the slightest doubt as to the accuracy of the statement 



VOL. XXVII, FART 2. NKW SI'R. X 



