Changes in Dorsal Vessel 79 



In the larger animals haemoglobin is chiefly important 

 as a means of carrying oxygen from one part of the body 

 "to another ; in the Chironomus-larva it seems to be rather 

 employed as a means of storing the oxygen. In either 

 case its usefulness depends upon its power of forming 

 a very loose combination with oxygen, which it takes 

 up easily, and easily parts with. Almost any reducing 

 solution, a stream of hydrogen or some other indifferent 

 gas, or diminished pressure, suffices to liberate much 

 oxygen from its temporary combination with haemo- 

 globin. Even in its crystalline form it gives oft' oxygen 

 readily, changing colour like the blood itself, and becom- 

 ing dichroic. 



Either the storage capacity for oxygen of the Chiro- 

 nomus-larva is considerable, or the oxygen must be used 

 very economically, for the animal can subsist long with- 

 out a fresh supply. One of us took a flask of distilled 

 water, boiled it for three-quarters of an hour, closed it 

 tight with an india-rubber bung, and left it to cool. 

 Then six larvae were introduced, the small space above 

 the water being at the same time filled up with carbonic 

 acid. The bung was replaced, and the larvae were 

 watched from day to day. Four of them survived for 

 forty-eight hours, and one till the fifth day, two of them 

 meanwhile changing to pupae. Nevertheless the water 

 was from the first exhausted of oxygen, or very nearly so. 



Dareste (1873) observes that in the pupa of Chironomus ciianges in 

 the dorsal vessel becomes contractile throughout, and vessel, 

 divided into chambers by valves. We can confirm this 

 statement, having found that in the abdomen of the pupa 

 and late larva the dorsal vessel is provided with several 

 pairs of opposite valves and ostia. The chambers contract 

 in succession from behind forwards. 



Following a suggestion made by Dareste, we may 

 point out that the larval heart of CMronomus dorsalis is 



