[willey] BRANCHIODERMA AND BRANCHIOTREMA 97 



The name Branchiotrema^ was introduced as a phyletic term 

 to include all animals possessing gill-clefts, whether functional or 

 not, at any period of their life-history (Willey, 1899). These are now 

 contrasted with Branchioderma which are the triploblastic inverte- 

 brates, containing both the Chitinophora (vermes, arthropods, 

 molluscs) of E. Perrier (1893) and the Echinoderma. 



That the cleavage between Branchioderma and Branchiotrema 

 goes very far back is rendered probable by the relationship which the 

 Echinoderma and Enteropneusta ("Balanoglossus") bear to each 

 other through their larval forms and body cavities. The special 

 analogy between adult echinoderms and vertebrates has also been 

 enlarged upon. E. Hseckel (1896) remarked that echinoderms 

 approach vertebrates above all in their peculiar skeletal system; 

 they are almost the only invertebrates which, like vertebrates, deposit 

 lime in great quantity in the corium and, by the union of calcareous 

 plates, produce a skeleton of dermal scutes. The placoid scales of 

 fishes and the cranial shields of the Stegocephali have' the greatest 

 resemblance to the dermal armour of echinoderms. Early in the same 

 year, E. W. MacBride (1896) made similar comparisons independently 

 concerning the skeletal and nervous systems. 



The Branchiotrema have pharyngeal respiration with endodermal 

 respiratory epithelium; the Branchioderma have cutaneous respira- 

 tion with ectodermal respiratory epithelium. In coelenterate animals, 

 both ectoderm and endoderm, amongst other functions, act as respira- 

 tory membranes. 



Amphibia still exhibit a vicarious functional relationship or 

 correlation between cutaneous and pharyngeal respiration, such as 

 may have obtained before the cleavage took place. Necturus, the 

 "Mud Puppy," has a pair of lungs and two pairs of gill-clefts, neither 

 of which functions in ordinary respiration. The lungs of Necturus 

 are first and foremost hydrostatic organs. When kept in shallow 

 water, two to three inches in depth, the animals will remain submerged 

 indefinitely. If placed under circulation (either in running water 

 or in water through which bubbles of air are passed) in a vessel cover- 

 ed with a perforated zinc plate, the plate being accurately fitted to 

 the jar and immersed in the water so that the imprisoned Necturus 

 cannot reach the surface, there is no diminution of activity. Under 

 these conditions of close confinement it often touches the zinc dia- 

 -phragm in its excursions, as if trying to reach the top; but this is an 

 escape-movement and is not the result of oxygen hunger. If placed 



^This term has since been accepted by Professor Butschli (1910), though in a 

 more restricted sense than was originally proposed for it. 



Sec. IV, Sig. 7 



