196 INVERTEBRATA CHAP. 



glass vessels in pond- water with a little pond-weed, they will live 

 for a considerable time, and the eggs will hatch out into larvae, and 

 these larvae can be reared through their complete development till 

 they attain the adult condition. 



When the larvae escape from the egg membrane they have an oval 

 outline, and are provided with a large, swollen, almost square upper 

 lip and three pairs of appendages. Of these, the first pair are inserted 

 in front of the lip, and each consists of a single branch divided into 

 three joints, of which the centre one is the largest. All three carry 

 long hairs at their ends. The second pair of appendages on each 

 side consists of a broad basal piece (protopodite) ; it carries a long, 

 inwardly directed hook, which nearly meets its fellow beneath the lip. 

 This pair of appendages is postoral. The distal portion of the limb 

 consists of two branches, an exopodite or outer branch, composed of 

 a basal piece and four joints, and an endopodite or inner branch, com- 

 posed of basal piece and two joints. The basal pieces of exopodite 

 and endopodite are more or less adherent. The third pair of append- 

 ages are quite similar to the second, but smaller in size ; the proto- 

 podite is longer in proportion than in the second pair of appendages, 

 and it has on its inner side a triangular outgrowth, which carries 

 one or two long, inwardly-directed bristles. This, like the corre- 

 sponding process on the second appendage, is masticatory in function. 

 The exopodite and endopodite consist as before of four and two 

 joints respectively, but the distal joint of the endopodite projects 

 inwards. These three pairs of appendages are moved by long, back- 

 wardly-directed muscles, which converge towards and are inserted 

 in a small area in the dorsal integument. 



The mouth leads into a vertical oesophagus which is provided 

 with constrictor and dilator muscles. This, from its cuticular lining, 

 is obviously an ectodermal stomodaeuni. It opens into the true 

 endodermal gut, which runs backwards nearly to the posterior end 

 of the animal ; here it opens by an orifice, guarded by a sphincter 

 muscle, into a short proctodaeum lined by cuticle and derived from the 

 ectoderm. In front of this opening the midgut gives rise to two 

 ventro-lateral pouches, which have an excretory function and are 

 filled with granules of uric acid. 



In the base of the second pair of appendages is the opening of a 

 sac which projects backwards at the side of the mouth. This sac, the 

 antennary sac, is also excretory in nature, and is homologous with 

 the similarly situated sac in Astacns. 



The nervous system consists of a praeoral brain, on which rest two 

 simple eyes, and a sub-oesophageal ganglion connected with it by a 

 pair of cords. The nerves for the second and third pair of appendages 

 are connected with the sub-oesophageal ganglion. 



The little larva was baptized Nauplius by Glaus (1858). The 

 name had been previously employed by the Danish naturalist, 0. F. 

 Miiller, for a later stage in the development, when four pairs of 

 appendages were formed ; he imagined this to be an independent 



