296 LOWER VERTEBRATES. 



fish two or three inches long," while others were yet spawning, and these young fish 

 were presumably the fty of those that had spawned tlie same year, only somewhat 

 earlier. In a few days after hatching they present a sti'iking appearance on account 

 of the enormous development of the pectoral and ventral fins. 



The last family of the order is that of the bat-fishes, or Maltheid^. Some have 

 the forehead produced forwards into a more or less elongated kind of snout, and the 

 first dorsal is reduced to a single short appendage which is lodged in a cavity under 

 the snout-like prolongation, and just above the mouth ; the mouth is horizontal and 

 transverse, and varies in size in the different species ; the branchial apertures are in 

 the superior axils of the pectoral fins, instead of the inferior, as in most of the others. 

 The best-known species is that generally called bat-fish {Malthe vespertilio). It is said 

 that the fish assumes an almost toad-like attitude on the ground, the head being 

 directed slightly u]iwards, and the tail stretching straight backwards and held up by 

 the anal fin, while the pectorals assume tlie function of hind legs and the ventrals of 

 fore ones. It is an inhabitant of the tropical and warm eastern American coast waters. 

 Several curious specimens of the family are inhabitants of the deep sea. 



The long roll-call of the fishes is finished ! It had been revised, and none but the 

 living retained, among the Teleosts at least. But our conception and knowledge of 

 the class would be deficient were no reference made to the dead, and without some 

 hints as to the genealogy of the chief groups. 



The ancestors of the fishes — but not fishes themselves — must have existed in the 

 earliest fossihferous periods of which we have knowledge. But they were soft-bodied 

 animals, destitute of internal as well as external skeleton. For unnumbered feons, 

 animals of rank as low as, or still lower than, the laiicelet, must have tenanted the 

 ancient seas, and, quite likely, even the rivers. All there was of skeleton consisted of 

 a long membranous substance running lengthwise in the body, and between the nar- 

 row channel serving for the passage of the nei'vous cord and the larger cavity con- 

 taining the viscera; there was even no rudiment of a skull ; there were but rudiments 

 of a brain and heart ; the branchire were represented by simi)le bars between lateral 

 slits in the front part of the intestinal canal ; all there was of fins consisted of median 

 and low anterior lateral folds; other ]iarts of the organization were equally inferior. 

 Such were of the class of Leptocaedians. It must have been long afterwards 

 when the longitudinal axial rod had become more developed, and in connection 

 thcrew ith a kind of skull came into being ; then also a more complicated branchial 

 skeleton had been developed ; brain, heart, liver, and other viscera had become spe- 

 cialized, and could have been recognized as such with readiness. The forms were 

 doubtless diversified and numerous; jirobably in most lateral folds continued, and in 

 some were jierhaps even differentiated into anterior and posterior fins. But all such 

 died out without leaving any yet discovered traces, and the only known representa- 

 tives are those of the class that has been named Myzonts and Maesipobeanchi- 

 ATES : those which have continued to the present time became elongated and eel-like 

 in form, and consequently lost entirely the lateral folds or fins ; furthermore they 

 become partial parasites, and doubtless to this habit the two widely distinct orders 

 represented by the hags and lampreys owe their continued existence. 



From some type of the group so represented were born forms which became more 

 and more developed ; scale-like indurations of the integuments supervened, a concres- 

 cence of the cephalic cartilages resulted in a " skull," jjcctoral and ventral fins 



