XI 



PEACTICAL HINTS FISHES 



565 



n umbers in the tow-net 

 I nit these are not so con- 

 venient for investigation 



on account of their re- 

 duced size. As there is 

 little doubt that the Tele- 

 ostei ha\v been evolved 

 out of ancestral forms 

 with large eggs investiga- 

 tions are particularly de- 

 sirable on those teleosts, 

 mostly freshwater forms 

 inhabit inu- warm climates, 

 in which the large size of 

 I he i-u- has been retained. 

 Then- is an important 

 tield for investigation in 

 the embryology of tropi- 

 cal freshwater fishes. Of 

 individual families the 

 Siluridae, Characinidae 

 and Gymnotidae - call 

 especially for investi- 

 gation. 



DIPNOI. The Lung- 

 fishes form a group of 

 much importance to the 

 Vertebrate morphologist 

 on account of, on the one 

 hand, their great an- 

 tiquity and the retention 

 of many archaic features 

 in their organization and, 

 on the other hand, of the 

 fact that they present to 

 us foreahadowinga of vari- 

 ous features which become 

 prominent characteristics 

 in the tetrapoda or 

 terrestrial animals. A 

 knowledge of their ern- 

 bryology consequently 

 ber.ame one of the great 

 desiderata of Vertebrate 

 Embryology. The first 

 discovered of the three 

 surviving representatives 

 of the group Lepido- 



at 

 Pf 





Kic. 'J'tO. Blastoderms and embryos of Trout 

 (Salmo fario). (After Kopsch, 1898.) 



iye; ot, otocyst ; p.f, pectoral tin ; rh, rlioinbenc. j hai-n 

 \pusivl surface of yolk. 



