ZOOLOGY. 341 



brains of a character which he expresses by the name he proposes for 

 the group, Lyencephala, or " loose brains." The mammalia with these 

 brains are the Monotremata (echidna and ornithoryncus) and the 

 Marsupialia. In both these groups the cerebral hemispheres are in 

 " a loose or disconnected state," as compared with those of higher ani- 

 mals. The marsupials are mostly nocturnal, or appear abroad during 

 the day only in dark, rainy weather ; and the Professor considers their 

 low position associated with the prevalent habit of limiting the facul- 

 ties of active life to the obscurity of night. The second ascending 

 type of brain is found among the Rodentia, Insectivora, Cheirop- 

 tera and Bruta, or Edentata;- and these Dr. Owen proposes to 

 call Lissencephala, or "smooth brains;" a name referring to the 

 smooth, unconvoluted exterior of that organ. The Professor pointed 

 out the numerous relations presented by this group to the oviparous 

 vertebrata, and remarked that the most ancient mammals whose fos- 

 sil remains were found in secondary strata were either Ly- or Liss- 

 encephalous, and belonged either to the Marsupialia or the Insectlv- 

 ora. The third type of brain was found in monkeys, lemurs, etc., 

 and named Gyrencephala, or "winding brains; " so called from their 

 convolutions. This division was subdivided into the Mutilata, so 

 called because their hinder limbs seemed, as it were, to have been 

 amputated, comprehending Cetacea and Sirenia ; the Ungulata, di- 

 vided into Perissodactyla and Artiodactyla, according to the odd or 

 even number of their toes, the single hoof of the horse, the triple 

 hoof of the tapir, exemplify the first ; the double hoof of the camel, 

 the quadruple hoof of the hippopotamus, the second, and the Ungui- 

 culata. The Professor pointed out the superior utility to man of the 

 members of this division now in existence, compared with the service 

 which could have been rendered if their predecessors in geological 

 time had survived down to the human epoch. The present rumi- 

 nants, for example, more thoroughly digest grass, and form out of it 

 a more nutritive meat, and the present monodactyled horse was a bet- 

 ter and swifter beast of draught than his tridactyle predecessor, the 

 miocene Hipporion, could have been. Passing from Quadrumana, 

 the fourth and highest type of brain rises at once to that " marvellous 

 structure which is peculiar to our own species ; " and the sole repre- 

 sentative of this class is Man, described as Archencephala, or ' over- 

 ruling brain." 



PHYSIOLOGY OF VISION. 



At a recent discussion before the Boston Society of Natural His- 

 tory, Professor Rogers remarked that he thought that the physiology 

 of vision was as yet but imperfectly understood ; vision bv corres- 

 ponding points of the two retinas, for instance, cannot be maintained, 

 though it is found in all treatises on physiology, and in most on 

 optics. 



Dr. Gould referred to the fact that though in strabismus there is 

 distinct vision with the normal eye, the other being unused, squint- 

 eyed-persons cannot get the stereoscopic solid image, but only see a 

 flat picture. 



Professor Rogers remarked that there is such a thing as being right- 

 eyed and left-eyed, as well as right-handed and left-handed ; indeed, 

 29* 



