Mr Purser, Preliminary notes on some Problems, etc. 63 
Preliminary notes on some Problems connected with Respiration 
in Insects generally and in Aquatic forms in particular. By G. L. 
PursER, Coutts Trotter Student, Trinity College. (Communicated 
by Mr F. A. Potts.) 
[Read 23 November 1914.] 
THE means by which the gases are carried to and from the 
respiratory organs, in the majority of Triploblasts, is the blood, 
which is a general carrier for all substances to be used or got rid 
of by the cells. These substances are usually simply dissolved in 
the serum, but oxygen, being often required in larger quantity, 
is also carried loosely combined with some substance which is 
situated in the serum or in special respiratory corpuscles. The 
two substances known to be respiratory in function are the 
pigments Haemoglobin and Haemocyanin, the former an Iron 
compound of a globulin, the latter a Copper one of like form. 
When, however, we examine the respiratory apparatus of an 
aérial Insect we find an altogether different arrangement, the 
reason for which is rather obscure. We do not, unfortunately, 
know from what stock or stocks the Insecta arose and have, 
therefore, little idea what the primitive insect was like, but still 
the origin of the tracheal system is a subject upon which it is 
interesting to speculate. 
Examination of the respiratory organization of a group con- 
taining both aquatic and aérial forms brings out the fact that the 
general method for aquatic members is evagination as a gill and 
for aérial members invagination as a lung, as for instance in Verte- 
brata. Fish have gills and the terrestrial members have lungs. 
Again in the Mollusca aquatic members of the Phylum, such as 
the Lamellibranchiata, have exposed gills, while in aérial members 
the mantlefold, used by so many aquatic ones to protect the gills, 
encloses a chamber which acts as a typical lung. 
Similarly in Arthropoda the aquatic forms, most Crustacea, 
have evaginations, gills, while the aérial forms, most Insecta, have 
invaginations, tracheae. The organ of respiration is therefore of 
the type that we should expect from an examination of other 
phyla. 
Another characteristic, which might well be expected in 
Arthropoda, is the serial repetition which is exhibited. Metameric 
Segmentation, which lies at the basis of the Arthropod Classifica- 
tion, is exhibited by almost every kind of organ in the animal’s 
body. Hence, what could be more natural than that the respiratory 
organ should follow suit and be serially arranged also ? 
VOL. XVIII. PT. II. 5 
