EESPIKATION" OF LAEVA 89 



intervals along the tube are long hairs, in several groups of twos and threes with 

 a common base. 



Another peculiar structure of the eighth segment are the lateral groups of 

 small scales which form large patches behind the middle. Behind these, inserted 

 on a small chitinized tubercle, are large fan-shaped tufts of ciliate hairs. Simi- 

 lar tufts are present, near the base of the breathing tube and also ventro-pos- 

 teriorly. 



The ninth segment is not in a plane "v\ith the others but is inserted upon the 

 eighth segment ventro-posteriorly, pointing obliquely downward. It is short 

 and its diameter is less than that of the other segments. In the final larval stage 

 it is in large part covered by a chitinous plate which completely surrounds it. 

 In the previous stages the plate is smaller, dorsal and saddle-shaped. Beyond 

 the plate the segment is fleshy, cushion-like with the anal opening in the middle. 

 Surrounding the anus are four cylindrical transparent appendages, the tracheal 

 gills. Dorsally, at the apex, the segment bears a group of very long setae which 

 are inserted upon two chitinous pieces. Ventrally and outwardly the anal plate 

 is excised to make room for a fleshy portion upon which is situated a remarkable 

 organ, the ventral brush. The ventral brush consists of a series of long fan- 

 shaped tufts with curved stems, inserted close together along the ventro-median 

 line. Each tuft hinges upon a slender transverse strip of chitin and, towards 

 the middle, where the tuft is inserted, these strips are thickened and perforated. 

 Outwardly these transverse strips are joined to a pair of longitudinal strips. 

 The tufts are not inserted exactly upon the median line but alternately a little 

 to one side or the other, thus showing the bilateral origin of the structure. 

 There are no muscles to control the ventral brush. Its function is that of a 

 steering or steadying apparatus. 



THE RESPIRATORY ORGANS. 



The respiratory system of the mosquito larva has been carefully investigated 

 by Easchke. His studies were apparently based upon larvae of two species, Culex 

 pipiens and a species of Aedes. We give herewith a translation of the part of 

 his paper dealing with this subject. 



" It is perhaps rarely that one finds in the insect world such many-sidedness 

 with reference to respiration as in our larva. We must here consider a stigmata! 

 respiration, an intestinal respiration, a respiration through the tracheal gills 

 and finally such a one through the external skin, therefore four different modes 

 of taking in gases. Naturally one of the mentioned modes will have to be con- 

 sidered as the most important and there can hardly be a doubt that this is the 

 stigmatal respiration, the breathing of atmospheric air by means of the siphon. 



" When the larvas were deprived of the opportunity to breathe air directly, by 

 confining them in a receptacle covered by gauze and placing this in an aquarium 

 so that it was entirely surrounded by water, they showed great unrest; after a 

 short time they shrank noticeably and died after about ten hours. 



" On account of the enormous exchange of gases the tracheal system is very 

 extensively developed. Two strong tracheal trunks extend from the apex of the 

 breathing tube of the penultimate body segment to somewhat before the middle 

 of the thorax, and these are united apically by a strong tracheal bridge. In 



