14 



^fiK'i'iilly |iro1ruil(' licfort' tlic lijis, sn tli;il tlic laltcr cMiiimt lif sfcii milsidc 

 the eyc, Init tliis forms a part ot' llic outliiie'-'); tliis l-ui be exprcsyeil alsu hy 

 sayiug tliut the eyes of tlic silvtT eels look mure to tlie sides thuii tliose oi' 

 tin' yelldw oiRs, \vl]ifli look more upwards. The eyes oi' tlic silver eels, 

 moreover, are MUich larger tlian those of the yellow oiie«. the largest diameter 

 of the eye, the horizoutal one, oftenest exceeding half the interorjjital sjjaee, 

 und in the males even very nearly equalling the whole interorbital space, and 

 sonietimes (fig. 6 a) being longer than the snout before tlie eyes. Among the 

 femaies, liowever, there is mneii variation in the latter measure, so tliat the 

 eyes are the lai'ger in proportion to the breadth of the front tlie smaller tlie 

 eels are; tliis evidently is nearly eonneeted Avith the faet that tlie interorbital 

 Space is greatest in the large eels. In order to show tlie extremes among the 

 large eels, two sucli of 307^ and35'/.iinchesin leugth are represented (fig. 3 A:4, 

 ]ilate I), tlie latter witli a broad front, the former with a narrow one. Thongh 

 tiie difference in the size of the eyes in proportion to the interorbital space 

 here is very distinct, such a difference is not very striking when the diameter 

 of the eyes is compared to the lengtli of tlie snout. The form witli u narrow 

 interorb. space, however, has decidedly somowliat larger eyes than that with 

 a large interorb. siaace. 



Among the males of the silver eels tliere is, as shown in tig. (i i^- 7, iilate II, 

 great difference in the form of tlie head; but the diameter of the eyes is al- 

 ways nearly or exactly as large as tlie interorbitafl space; the tip of the snout, 

 on the Ilther liand, is now pointed. now siiublied, and there caii, upon tlie 

 whole, be a very considerable difference in the si/.e of the head; Imt in no case 

 of which I kiiow eau we find an appearancc wliicli, like that of the femaies. 

 reseiii))les the ajipearanct' oi the frog-niouthed eels (Hg. 1, plate I). 



There is no doubt that lig. 4, plate 1, represents a female eel whose head 

 wliiii it was yoimger has looked something like that of the frog-mouthed eel 

 rej^resented in lig. 1, plate I, The changes wliicli have takcii jilace in it siiu-e 

 tlien are cliietly the followiiig: The head liefore the eyes, whei'c the olfactory 

 organ lies, has grown higher; the eyes have become several times larger lu 

 volunie. and have tnnied in such a way that tliey look more to the sides; the 

 head. ujion Ihc wlidle. has become fatter aii<l jiluniper, Tlic lnwer jaw seems 

 to liuA'e grown a little lunger by tlic forniatioii di a suft point at its foremost 

 end; the occipital niusck'S are iio longer protrndiiig, l'oi- llie whole body of the 



*) Tilis i.s still iiiiirc i-(]iis]iii iiiiiis liclinc thr cl'Is :irc plnrccl in s|iiiit: :ill Ilic IIl'uivs, 

 ncvertlidi'SH, .slmu Ihc saaic, lliijiij,'li llicv luivc liccii iliiiwn linm eds wliicli :in- 

 l<c|i1 iii s|iirit. 



