Literary Notices. xi 



a more or less perfect state of development in all Amphibia at some 

 period in their life-history. 



" In the urodela the distribution may readily be reduced to the 

 following type : Upon the body, three lines, a lateral continuous or 

 not continuous with an occipital group, though not continuous with the 

 orbital lines ; a ventral line extending from under the arms in the pec- 

 toral region to near the hind legs ; a dorsal line somewhat closely con- 

 nected with the lateral at its cephalic end and seldom extending as far 

 as the level of the vent. Upon the head, a series extending from be- 

 hind the eye, above and below it to the snout, the supra- and infra- 

 orbital lines ; a line upon the lower lip, the oral, connected with the in- 

 fra-orbital by the angular ; a line from the angle of the mouth to the 

 lateral corner of the head and there meeting a diverging line upon the 

 ventral side of the head, and, when this is sufficiently developed, a 

 line or trend of organs upon the side of the head ; these the jugular, 

 gular zwdi. poslorbitalXiwQ^ of the descriptions and figures. 



" Comparison with other Ichthyopsida may not be of much value; 

 however, the distribution approaches most nearly that in the Dipnoans, 

 then in Elasmobranchs ; among the latter Chlamydoselachus , apparently, 

 in the greater extent of the gular line, shows most resemblance to the 

 Amphibia. 



"The significance of the arrangement into groups is apparent 

 when the system is examined in the larva at different periods of devel- 

 opment. Evidently, as has already been maintained by Malbranc, 

 each group sprang from a single organ by repeated fission in the same 

 plane. His figures and my own observations clearly show that such is 

 the case, as illustrated by Fig. 45. Exactly how this takes place, how- 

 ever, is unknown. Whether the sensory cells may arise from the sup- 

 porting cells, or from sensory cells alone, and supported from support- 

 ing cells or from ordinary epidermal cells, yet awaits solution. 



" Malbranc called attention to the often recurring arrangement of 

 groups upon two coordinates perpendicular to each other, or nearly so 

 (as in the gular line), pointing out the physical advantage in such an 

 arrangement in perceiving the direction and strength of a vibration in 

 the water, should such be their function. In Ichthyopsida, in which the 

 sense organs are deeply sunken in canals, the pores often become many 

 times divided. In Amia, Allis found that the primitive pores divide 

 quite regularly in a certain plane for a number of times ; these second- 

 ary pores again often divide in a plane at an angle to the first, generally 

 a right angle or nearly so, reminding us of the groups in Amphibia. 

 In forms, then, in which the sense organs are confined in canals, this 



