1894-1 THE BRITISH NATURALIST. 255 



into the water, for its motion was too rapid for careful observation, but 

 it is very certain that its normal condition is bent up in this form : Q. 

 The large mouth is furnished with many small bristles and maxillaries 

 and some other flat organs which moving horizontally are kept in 

 constant activity; there are two large ones in the upper and two in the 

 lower jaw. These are serrated on the outer edge, and appear open 

 tubes through which I fancied water entered. Between the two 

 larger tusks there are some minute teeth shaped like a fan, intended, 

 I fancy, to serve the same purpose as the saw-like organs in the mouth 

 of Covethra pliimicomis (Fig. 5 c, plate V., page 107). The two eyes are 

 very noticeable in the centre of the head on either side. When you 

 have the head under the microscope they can only just be seen, but 

 when you take a side view they are very distinct, and the cavity is also 

 clearly seen from which the antennae or tufts are protruded. These 

 De Geer calls barbillons ; they are formed like brushes composed of a 

 large number of different kinds of bristles split at the extremities and 

 opened out. The whipping action of these hairy tufts is most curious 

 and effective, for when the Dixa wishes to draw in nourishment the 

 head is turned right back on the dorsal side and the tufts instantly 

 begin to play. The neck joining the head to the first segment is very 

 loose and flexible. I cannot yet satisfy myself whether the head is 

 twisted half round or simply laid back, for the authorities are com- 

 pletely at variance as to which is the upper and which is the lower 

 lobe of the head. Stoeger, differing from Reaumur and De Geer, says 

 " A brush of fine bristles springing up from the front and upper 

 part of the sides extends over the head," while the most recent 

 investigator, Professor Meinert,* asserts that "the larva of Dixa 

 procures its food in the same manner as the larva of Anopheles, 

 making use of its rotatory organs to put the water in motion. It 

 cannot at any time bend round its head like this larva, but rather 

 bends it back in such a manner that the summit of the head nearly 

 touches the upper surface of the thorax." Now I want some of your 

 readers who may be lucky enough to find this larva to try and settle this 

 point, for I am still in doubt whether the head is not turned round as in 

 Anopheles, though I must say I don't think so. The question is whether 

 the tuft of protrusile hairs is a beard or a " top-knot." If Stoeger 

 is right, then the eyes are placed, though near the centre, yet certainly 

 in the lower lobe of the head, and I don't know another instance oi 

 a similar kind. We have heard a good deal about the "pineal" eye 

 found near the top of the head in the vertebrates, and recently we 

 have heard from Mr. Hornell of the third eye in the Copepod, 

 Monstrilla Anglica, found on the Jersey coast, but he writes me in 



*■' Eucephalous Larvae" — Proceedings of the Royal Society of Copenhagen, 1885-6, 



page 486. 



