12 



posteriorly. These rudimentary gills are especially interesting because 

 DR. LAUTERBORN* has also found a larva possessing gills (only in 

 his case fully developed) arising from the tenth segment. 



In LAUTERBORN'S Larva I. they resemble mine very closely, in his 

 Larva II. they are much larger. So here we have a species combining 

 in one larva both types of ventral blood gills. These facts I think 

 show that the ventral gills are morphologically of very little constancy 

 compared with the anal gills, and I may also mention that the presence 

 of red blood is no indication of their presence, for one larva of the 

 " Pusio " group, resembling the blood-worm superficially, is quite devoid 

 of them, as is also C. niveipennis.^ So it is hardly possible to use the 

 two characters, red blood and ventral gills, as indicative of a distinct 

 group of larvae, as was suggested by MEINERT. 



THE HEAD. 



The head of C. pnsio is a wonderful object, when viewed through 

 the microscope with a fair magnification, and I should think it 

 would be hard to find a Chironomid more suitable for examination than 

 this species. The chitin is sufficiently dense to enable all the parts to 

 be clearly contrasted and denned, and at the same time transparent 

 enough to let them be seen by transmitted light. 



The following details can all be made out in the living larva. A 

 good plan is to place the larva in a Ross or other accurately adjustable 

 compressorium, and retain it under slight pressure in such a position 

 that the various appendages are spread out to their full extent. 



The head including the extended labrum, is -26 mm. long by 

 2 mm. broad and may be described as dark amber in colour. It is 

 composed of a medium dorsal clypeus, and the two lateral epicranial 

 plates which curve round the head to meet each other on the ventral 

 surface in their anterior part, while behind a large open space or bay 

 remains. This allows the head to be easily flexed on the ventral 

 surface of the thorax. The clypeus is a narrow oval plate of somewhat 

 irregular outline. Near the anterior edge arise a pair of chitinous 



* LAUTERBORX. Zoologischen Anzeiger Bd. XXIX., No. 7. 

 t MIALI. The Harlequin Fly, pp. II and 13. 



