70 MR WILLIAM TURNER AND DR H. S. WILSON ON THE 



fringed with a number of short, closely-set teeth. The plates gradually come 

 to a point at their free extremity. The basal segment has a well-marked tubercle, 

 bearing two or more conical papillae projecting from it, close to its junction with 

 the terminal segment. 



Each of the second pair of jaws (Maxillae, Rathke) also consists of two 

 segments (fig. 6, d). The terminal is formed of but a single thick plate, which, 

 very slightly curved, comes to a fine point at its free end, and bears upon its 

 posterior margin a row of closely-set pointed teeth, somewhat longer and more 

 pointed than those of the first pair. The basal segment is longer than that of the 

 first pair, and supports an elongated body, pointed like a style, which, like the 

 terminal part of the jaw, projects towards the ventral mesial line. A short 

 stunted papilla, corresponding in its character to those of the first pair of jaws 

 and of the antennie, projects from the base of the style. 



Each of the third pair of jaws (Kieferbeinen, Rathke), much longer than the 

 first and second, consists of three segments (fig. 6, e). The terminal segment is 

 formed of a chitinic plate, pointed at its free. end, and totally devoid of teeth. It 

 articulates with the middle segment, which is partially embraced by a peculiarly 

 folded chitinic plate, having on its firee margins a row of bristle-like projections. 

 It would appear as if the middle segment, by the contraction of the muscular 

 apparatus connected to it, could, together with the base of the terminal seg- 

 ment, be drawn between the laminse of the folded plate. The basal is the 

 largest of the three segments. It contains two muscles, a flexor and an ex- 

 tensor, for the movement of the second segment upon it. 



The cephalic is separated from the thoracic part by a constricted portion, 

 which, for descriptive purposes, we may term the neck (fig. 1, t), but which, 

 morphologically, is probably to be regarded as the first thoracic segment, for the 

 first pair of limbs is connected to its under surface. The thoracic part consti- 

 tutes by far the largest division of the animal. Projecting from its dorsal and 

 ventral surfaces, and from its sides, are a number of processes, which give to the 

 animal its characteristic appearance. The lateral processes form lappet-like pro- 

 longations. On each side they are five in number, and consist of two pairs and 

 a terminal single process. The two processes in each pair consist of a larger 

 anterior lappet extending downwards and backwards, and of a smaller posterior, 

 upwards and backwards. The terminal lateral process passes also downwards 

 and backwards, and, with its fellow on the opposite side, gives to the animal 

 the peculiar forked appearance which distinguishes it posteriorly. The sides 

 of the thorax, immediately behind the origin of the smaller posterior lappet of 

 each pair, present two slight constrictions, which would appear to indicate its sub- 

 division into three smaller segments ; if to these we add the neck, four thoracic 

 segments are indicated. The dorsal mesial processes we find to be seven in 

 number ; and in this particular we agree with the earlier observers, Johnston 



