126 ME. J. M. BROWN ON THE ANATOMY OF 



The Larva of Tipvla maxima. (PI. 24. fig. 1.) 



This larva, a form of " leather-jacket," is found beneath stones, either close to or 

 in the bed of streams, at almost all seasons of the year. It is a vegetable feeder, 

 consuming leaves and roots of grass, and also apparently swallowing quantities of soil. 

 It is a sluggish creature, burrowing in the damp earth, and its burrows can be followed 

 for some distance. It pupates about June, in the earth, and emerges during July 

 or August. 



The larva, when- full-grown, is about 1J inches in length. It presents the following 

 external features :-- 



1. The strong chitinous capsule (" head ") bears the jaws and serves to support the jaw-' 

 muscles, but does not contain the " brain." 



2. The trunk is composed of 11 segments, more or less similar to each other, with 

 the exception of the posterior one. The head-capsule is completely retractile within the 

 first segment. The segments increase in size towards the middle of the body, where 

 they become indistinctly ringed externally into two ; but this division does not correspond 

 to internal segmentation, except that the alary muscles of the " diaphragm " are 

 attached to the body-wall at the extremities and also at the middle points of the 

 segments (PL 27. fig. 19). The hindmost segment is different from the others, and, 

 besides bearing the anus ventrally, appears to be modified in relation to respiration. 

 No indications of limbs occur on any of the segments. 



The hindmost segment (PI. 24. figs. 2, 3, 4, & 5) is obliquely truncated behind. This 

 truncated region, which is surrounded by three pairs of flattened triangular processes, 

 bearing along their margins a fringe of strong hairs (ni.f.), includes the two spiracles 

 (sp.), which appear as dark, broadly-oval spots, lying within a somewhat saucer-shaped 

 depression. By the folding inwards of the processes or lobes the spiracles can be 

 completely enclosed within a cavity, the stiff fringe serving to contain an air-bubble at 

 the same time. This generally occurs when the larva withdraws itself beneath the 

 water. Each of the dorsal lobes bears in addition to the marginal fringe a specially 

 long sensory hair (s.h.) at its apex, and three others (s./j.J symmetrically arranged, but 

 of different character from the first one. The structure of the spiracles is described 

 below. 



The ventral surface of this segment (PI. 24. fig. 3) carries the anus (a.) in the midst 

 of a raised and somewhat swollen area. This raised area serves also to give origin to 

 four pairs of hollow, unjointed, palp-like processes (PI. 24. figs. 2, 3, & 4, b.g.). Two 

 pairs, one anterior to, and the other lateral to the anus, are long, tuhe-like structures 

 tapering towards their extremities, freely movable and specially extended when the larva 

 is below water. Two much smaller pairs — in fact, mere pointed outgrowths — occur 

 in positions shown in the figures. From their structure and relations these seem to 

 serve as " blood-gills.'' They contain each a branch of the tracheal system, and a strong 

 flow of blood is maintained through them. They are not present in the common leather- 

 jacket (T. oleracea), which lives in fields, while in the larva of T. eluta they are still 

 more prominent, the larva being more completely aquatic. 



