15 



Exuviation now continues at intervals of a few days up to and 

 during adult life. The cast skin has a most perfect resemblance to 

 the animal it has left, the minutest structures being retained in the 

 cast. The suckers alone appear to be shed separately from the body 

 structures. I have observed ten moults in the same individual, but 

 the length of time elapsing between these is longer as the season 

 advances and the temperature is lower. The early development 

 also of ail organs in the young is largely influenced by the chances 

 of feeding and temperature. Opinions vary as to the age at which 

 the larva enters the second stage ; Claus mentions five days, and 

 Baird six days after hatching, but my observations go to show that 

 the first moult takes place on or before the third day. 



Structural Description and Organisation. 



The carapace or shield is of a transparent greenish hue, cordate 

 in shape, the anterior margin being rounded off, the posterior having 

 a deep A-shaped indentation, the angle of which is occupied by the 

 thorax. 



The eyes are of a deep violet colour, enclosed in a membranous 

 sac, and are areolar, like those of the Branchiopod^e (Fig. 7). They 

 are situated on the dorsal surface of the carapace immediately below 

 the antennae. This pair of eyes (for there exists another eye) consists 

 of about forty facets or kernel-shaped crystalline bodies in each eye; 

 the dark pigment patches radiate from the base in five rows, the 

 interstices being of a greenish-yellow colour. There is a channel 

 surrounding each, through which may be seen blood bodies in 

 motion. The eye itself is capable of a slight twitching, rotary 

 movement. The single eye above referred to has three convex 

 corneal lobes encircling a triangular mass of dark pigment, and is 

 placed in the middle line of the carapace on the dorsal surface, just 

 above the mouth, at the apex of a triangle having for its base the 

 paired eyes. Baird apparently described this organ as the brain, 

 but its lenticular structure shows it to be without doubt an auxiliary 

 eye. 



The antennae are on the ventral surface of the carapace immedi- 

 ately above the paired eyes, but nearer to the middle line (Fig. 8). 

 They consist of two pairs, the upper pair having three joints each, 

 the lower four joints. Attached to the upper pair are a pair of 

 acutely curved hooks having sharp points. Under the microscope 

 they are seen to be traversed by a channel. At their bases are four 

 hard, chitinous teeth. The structural difference between male and 

 female antennae is slight ; the latter are the larger of the two. 



The mouth or siphon is a curious structure, and occupies a 

 central position below the single eye. It has the appearance of a 

 prominent pouch, and bears two pairs of mandibles and maxillse. 

 These are minute, transparent, serrated plates, which are placed at 



