LEPTOCEPHALI. 181 



two lateral caeca. The intestine is straight, running close to 

 the abdominal profile, with a small appendix directed for- 

 ward and a larger one directed backwards. The vent is 

 nearly always very small, and, in preserved examples at 

 least, cannot always be discovered. Its position is vari- 

 able, even in examples entirely similar in other points. Air- 

 bladder none. No trace of generative organs. 



The vertical fins, when present, are confluent, with more 

 or less conspicuous traces of rays ; sometimes they are merely 

 a fold of the skin, without any rays. Pectoral fins some- 

 times present, sometimes rudimentary, sometimes entirely 

 absent. Ventrals none. 



Most examples have series of round black dots along 

 each side of the abdominal profile, along the lateral line, and 

 sometimes along the dorsal fin. They remind us of the lumi- 

 nous organs of many ScopelidcB, Stomiatidce, and other pelagic 

 fishes, but are composed entirely of pigmentary cells. 



These fishes are found floating in the sea, frequently at a 



great distance from land. Their movements are slow and 



languid. The largest specimen of Leptocephalus observed 



was 10 inches, but specimens of that size are very rare. 



[See Kblliker, Zeitschr. wiss. Zool. iv. 1852, p. 360 ; and Cams, Ueber 

 die Leptocepialiden. Leipz. 1861. 4to.] 



Taking into account all the various facts mentioned, we 

 must come to the conclusion that the Leptocephalids are 

 the offspring of various kinds of marine fishes, representing, 

 not a normal stage of development (larvae), but an arrest 

 of development at a very early period of their life ; they con- 

 tinue to grow to a certain size without corresponding develop- 

 ment of their internal organs, and perish without having 

 attained the characters of the perfect animal. The cause 

 by which this abnormal condition is brought about is not 

 known ; but it is quite within the limits of probability that 

 fishes usually spawning in the vicinity of land sometimes 



