78 The Larva of Chi'ronomus 



worms (such as the earthworm, Tubifex, Nais, Capitella 

 capiiafa, in corpuscles, Terebella, Arenicola, &c.), gephy- 

 reans, crustaceans (among others Daphnia and Chiro- 

 cephahis), the burrowing bivalve mollusk, Solen legu- 

 men, Planorh'is corneiis, Limnaeus, Paludina, Littorina, 

 Aplysia, Patella, and Chiton. It seems to be absent 

 only from the larval Muraenoids among vertebrate 

 animals. Lankester ^ long ago remarked that haemo- 

 globin occurs where increased facilities for oxidation are 

 required, as by burrowing animals and inhabitants of 

 stagnant pools, especially such as lurk in foul mud. It 

 also occurs in animals which are particularly active, and 

 in tissues which are frequently exercised (voluntary 

 muscles of vertebrates, jaw-muscles of snails, &c.). It is 

 well develo23ed also in large thick-skinned animals with 

 limited respiratory surface (vertebrates). Pelagic animals, 

 which are of soft texture, usually of small size, and there- 

 fore with a relatively large surface, and which need above 

 all things trans23arency so that they may escape the 

 notice of their enemies, are nearly always i]l-suj)plied 

 with haemoglobin, or more commonly want it altogether. 

 Certain Chironomus-larvae and various closely allied 

 Dipterous larvae have no haemoglobin, and it is to be 

 observed that these usually haunt the surface of the 

 water, or at least do not bury themselves in mud. 

 Thus the surface-feeding gnat-larva, and the phantom- 

 larva (Corethra), which j^oises itself in the middle depths 

 of clear water, have no haemoglobin. "We cannot, how- 

 ever, explain on these or any other principles all the 

 cases of presence or absence of haemoglobin in particular 

 animals. We cannot tell, for instance, why caddis-worms 

 or the larva of Dicranota, living in the same streams as 

 red Chironomus-larvae, and leading a very similar life, 

 should have no respiratory pigment at all. 



' 1873, p. 9. 



