MULTICELLULAR ANIMALS 



169 



larval Amphibia, for example frog tadpoles, the digestive canal is 

 perforated on either side in the region of the pharynx by a series of 

 slits (Fig. 112) equipped with gills. In the fishes water is taken in 



OPERCULUM CUT AWAY 



GILL CUT AWAr 



GILL SLIT 



GILL FILAMENT 



Fig. 112. — The respiratory system of the common perch. The operculum or shield 

 has been cut away to disclose the gills and gill slits. 



through the mouth and passes out through these slits, bathing 

 finely divided filaments, which line the slits and are extensively 

 invaded by blood vessels. In the adult Amphibia that have gills, for 



Fig. 113. — Necturus, the common mud puppy, found in the Mississippi River and 

 its tributaries. In life the gills stand out about the head as a bright red ruff. 



example Necturus, the mud puppy, the gills are extended like a 

 ruffle into the surrounding water (Fig. 113). In the dipnoids, the 

 so-called lung fishes of South America, of Australia, and of Africa, 



