GNATS MIDGES 469 



amongst the mud. Some of them, provided plentifully with 

 haemoglobin, are in consequence able to live at great depths, it 

 is said even at 1000 feet in Lake Superior, and come to the 

 surface only occasionally. A few are able even to tolerate salt 

 water, and have been fished up from considerable depths in the 

 sea. It is a remarkable fact that these physiological capacities 

 differ greatly within the limits of the one genus, Chironomus, 

 for some of these species are destitute of haemoglobin, and have 

 to live near the surface of the water ; these have a superior 

 development of the tracheal system. The pupae of Chironomus 

 have the legs coiled, and the thorax, instead of being provided 

 with the pair of tuljes or trumpets for breathing that is so 

 common in this division of Diptera, have a pair of large tufts 

 of hair-like filaments.^ A very curious form of parthenogenesis 

 has been described by Grimm ^ as existing in an undetermined 

 species of Chironomus, inasmuch as the pupa deposits eggs. 

 Although this form of parthenogenesis is of much interest, it is 

 not in any way to be compared with the case, already referred to, 

 of 3Iiastor (p. 4 6 1 ). The " pupa " is at the time of oviposition prac- 

 tically the imago still covered by the pupal integument ; indeed 

 Grimm informs us that in some cases, after depositing a small 

 number of ova, the pupa became an imago. This partheno- 

 genesis only occurs in the spring-generation ; in the autumn the 

 development goes on in the natural manner. The case is 

 scarcely entitled to be considered as one of paedogenesis. 



Gnats of this family, and believed to be a variety of Chiro- 

 nomus jjlu^nosus, are subject to a curious condition, inasmuch as 

 individuals sometimes become luminous or " phosphorescent " ; this 

 has been noticed more specially in Eastern Europe and Western 

 Asia. The whole of the body and legs may exhibit the luminous 

 condition, but not tlie wings. It has been suggested by Schmidt 

 that this condition is a disease due to bacteria in the body of 

 the gnat.^ 



Cerato])ogon is a very extensive genus, and is to some 

 extent anomalous as a member of Chironomidae. The larvae 

 exhibit considerable variety of form. Some of them are aquatic 



^ For an extremely interesting account of Chironomus refer to Miall's book, 

 already cited, and, for tlie larva, to the valuable work of Meinert on Eucephalous 

 larvae of Diptera, Danske Selsk. S'kr. (6) iii. 1886, p. 436. 



- Ann. Xat. Hist. (4) viii. 1871. p. 31. ^ Ihid. (6) xv. ISP.'i, p. 133. 



