13 



the female by the absence of the ovary and the two black spots on 

 each lobe of the tail, which are so evident in the female even at an 

 early stage. 



Dci'dopmcnt and Metarnorphosis. 



The egg(Fig. 2) is of a spherical ovoid shape, measuring "35 mm., laid 

 in rows three to six in breadth, of a pale yellow colour, and glued to 

 its neighbour with an albuminous material. A\'hen freshly laid the 

 egg is quite soft, and whitish opacjue in appearance. The albuminous 

 matter rapidly becomes coagulated, and is seen to spread over and 

 extend outside the rows of eggs in short, ribbon-like processes, 

 obviously for the purpose of adhesion to the object on which the 

 eggs are laid. The egg is composed of three layers — the outer, tough, 

 granular, and slightly brown in colour ; the middle coat, which is 

 much thicker, is more transparent, though somewhat granular in 

 texture ; the inner coat being transparent and membranous. The 

 egg mass has the appearance of closely agglutinated starch granules 

 almost crystalline and transparent. Previously to hatching, the eyes 

 of the larva may be plainly seen, about the fifteenth day after 

 oviposition. The contained larva makes its exit from the upper 

 surface of the egg by cutting a longitudinal slit, the tail end first 

 emerging. 



The newly emerged larva (Fig. 3) measures '8 mm. in length, and 

 immediately sets forth in quest of a host, to which it attaches itself and 

 commences feeding. Even at this early stage it is well provided 

 with organs for this purpose, although in a much modified degree. 

 The eyes are relatively large. The swimming-feet are undeveloped, 

 their functions being undertaken by two pairs of limbs bearing sets, 

 and situated at the base of the eyes. These give to the larva a 

 darting motion similar to the Daphnia. A powerful pair of triple- 

 barbed hooks or foot-jaws (which are replaced at a later stage by 

 suckers) answer the purpose for attachment to the host. There are 

 two pairs of antennae — the anterior, or first pair, consists of a simple 

 hook bearing on one side of its base an organ resembling a palpus, 

 its function being probably the same ; the second pair has three 

 joints terminated by a claw, and united at its base to the first pair of 

 swimming setae. I have no doubt that these two pairs of clawed 

 antennae are the means by which the larva makes its exit from the 

 egg. Of these setse, the anterior pair at the base of the second 

 antenna are situated on a stalk, and are four in number of equal 

 length, with one smaller. Each of these is finely covered with 

 minute cilia, and, being articulated at the base, may be moved in 

 any direction by the owner. The second pair of sette are at the 

 base of the first pair of foot-jaws, and adjoin the mouth organs; they 

 bear three set?e each as above. In this larval state tlie modification 

 of the antennre into swimming organs is a character of the larva; of 

 the higher orders of Crustacea. The second pair of foot-jaws in the 



