HJEMOGLOBIN 189 



this butterfly. It is probable that pigments of the flavone type 

 are widely spread among insects, but the subject has been very 

 little studied. 



2. Haemoglobin and Allied Pigments. The chlorophylls (sensu 

 str.) are pigments with a tetrapyrollic nucleus and whose 

 integral metallic constituent is magnesium. Recent research 

 has demonstrated the chemical affinities between chlorophyll 

 and haemoglobin, each having as a base the substance termed 

 jDorphyrin, composed of four pyrrol groups in complex linkage. 

 It is possible, therefore, that haemoglobin is ultimately derivable 

 from chlorophyll, and that in the processes involved in animal 

 evolution the latter pigment has become profoundly transformed 

 so as to assume new functions, and its metallic constituent 

 magnesium has become replaced by iron {vide Fulton, 1922). 

 Among insects there are three types of pigments of this character 

 whose metallic element is iron, viz., haemoglobin, cytochrome and 

 certain red pigments of Lepidoptera. 



Haemoglobin is of rare occurrence among insects and it is only 

 in certain Chironomid larvae that it plays any part in coloration. 

 Among these insects it is well known to be present in the blood 

 plasma, and not in the blood-cells, and since Chironomid larvae 

 possess a transparent integument it imparts to them their char- 

 acteristic red appearance. Haemoglobin also occurs under localised 

 conditions in a few other insects, notably in the peculiar tracheal 

 end-cells of the larvae of Gastropkilus ; Hungerford (1922) has 

 also shown that it is found in the Notonectid Buenoa, and Mrs. 

 Brindley has recently (1929) recorded its presence in the accessory 

 genital gland of the male of Macrocorixa geoffroyi. The important 

 work of Keilin (1925) on the intracellular respiratory pigment 

 cytochrome, which is apparently of general occurrence in the 

 animal kingdom, shows that in the possession of this pigment 

 insects already have the chief constituents from which haemoglobin 

 may arise. The existence of haemoglobin, therefore, in the isolated 

 instances just enumerated does not necessarily imply any pro- 

 found physiological difference between them and other insects 

 devoid of this pigment. Since cytochrome plays no direct part in 

 insect coloration it does require further consideration here. 



