QUARTERLY CHRONICLE. 173 



that the tooth called canine in the upper jaw is no canine at 

 all. Unaccountably^ Mr. Bate comes to the conclusion that 

 Professor Owen's formula is the right one — a conclusion from 

 which, on a former occasion, we dissented. 



"Researches on the Compound Eyes of Crustacea and 

 Insecta." (Untersuchungen iiber die zusammengesetzten 

 Augen der Krebse und Insecten.) By Max Schultze. 



" The percipient elements of the retina," as the author 

 observes, " both in Invertebrate and Vertebrate animals pos- 

 sess a definite structure adapted to the function they have to 

 perform, and as this, in both cases, is the perception of one 

 and the same motion in the waves of the ether upon which 

 all luminous imj^ressions depend, it is, prima facie, probable 

 that the structure in question would be essentially alike. 

 Another question, however, arises — whether we are at the 

 present time or ever shall be able to discover by means of 

 the microscope the actual physical conditions upon which it 

 must be presumed the percipient power of the termination of 

 the optic nerve depends. For although we know the length 

 of the undulations, and are able easily to measure them, the 

 difficulty still remains of reconciling the enormous rapidity 

 of their recurrence with what we know respecting the rate 

 of perceptivity through the nerves themselves ; a difficulty 

 which would seem calculated much to lessen the hoj^e of our 

 being able to discover any relation between the visible struc- 

 ture and the undulations of light." 



The discovery, however, by the author, of the universal 

 existence of a very regular, laminated structure in the outer 

 segments of the " rods " and " cones " of the retina in man 

 and other Vertebrata,* affords an inkling of the direction 

 in Avhich we may look for some definite view with respect to 

 a purely mechanical theory of Kght- and colour-perception. 

 If Zenkerf is right in considering that in the case of the re- 

 flection of light in the laminated structure of the rods, which 

 may be compared to a set of glass-plates, a system of 

 statical waves must be estabhshed (which can only take 

 place, for the different coloured rays, where the reflecting 

 surfaces are at the proper distances apart), we may arrive at 

 some idea as to how the varying length of the undulations of 

 the different coloured rays is perceived irrespective of their 

 enormous rnpidity. 



In this view the laminated structure of the percipient rods 

 would seem to be of fundamental importance, and the author 



* 'Arcliiv. f. microscop. Anat.,' Ill, 1867, p. 215. 

 t 'Versuch einer Theorie der Farbenperception.' 



