82 F. G. HALL. 



For example the percentage composition of the three gases, 

 nitrogen, oxygen, and carbon dioxide, is quite different in the 

 swimbladder from that present in the atmosphere. Thilo does 

 not explain how the degeneration of the ductus pneumaticus 

 in the Physoclisti can be correllated with their ability to change 

 their specific gravity. 



The second class of theories contains three distinct views as 

 to how the bladder-gases are derived from the blood stream: 

 (i) those which suppose that the blood gives up its gaseous 

 constituents more or less directly to the bladder, the gas passing 

 directly from the blood into the bladder lumen; (2) those that 

 suppose that the gas gland is a pumping organ that is able to 

 force gases from the blood into the swimbladder gland; and 

 (3) those that hold that the gases of the swimbladder are derived 

 from the cytoplasmic decomposition of the gas gland cells. 



The first view which is often associated with the name of 

 Moreau (1877), is now quite out of date, although references 

 are often made to it in textbooks and other works of general 

 nature. The second and third views are still current and have 

 excited much controversy. Both of these suppose that the gas 

 gland is the special organ which extracts the gas from the blood. 

 They have been held for several years with great tenacity by 

 schools represented by Jaeger, and opposed by the adherents of 

 Nusbaum and Reis. 



Jaeger (1904, 1908) holds that the gas gland is primarily a 

 pumping apparatus, an apparatus for pumping the gases con- 

 tained in the blood into the swimbladder cavity. He further 

 supposes that the disintegration of a certain percentage of red 

 blood corpuscles is effected by secretions from the gas gland cells 

 a toxin being poured into the blood for this purpose. 



Nusbaum (1907) and Reis (1906) as a result of extensive 

 studies of the cytology of the gas gland have formulated certain 

 peculiar views as to its functions. They contend that gas bub- 

 bles are produced by actual decomposition of the substance of 

 the gas gland cells, just as gases are produced by putrefaction. 

 They also believe that erythrocytes are taken into the cells of 

 the gas gland and decomposed, oxygen being liberated and used 

 for such decomposition. There are many objections to such 

 a theory. For example, nitrogen is not known to be formed by 



