82 JOURNAL OF MARINE ZOOLOGY AND MICROSCOPY. 



tubular and emit a secretion formed by two unicellular glands 

 (fronto-lateral glands, Fig. 6 ; cf. also Fig. 16) on each side. Arti- 

 culating with the hinder end of the carapace is a caudal spine (c. s.), 

 which is moved by means of a muscle (t. f.m.) in a vertical plane 

 together with the tail or rudiment of the thorax and abdomen, and 

 helps to steer the larva. On the lower side is seen another charac- 

 teristic organ of the Nauplius — the huge labrum or upper lip (Ibr.) 

 This projects below the mouth (Fig. 9), and is furnished at the apex 

 with four unicellular glands (Fig. 5) which emit minute secreted 

 spherules. In front of the labrum is seen the black Nauplius-eye, 

 another characteristic Entomostracan feature, rarely seen in the higher 

 Crustacea or Malacostraca. At the sides of the Nauplius-eye are 

 seen a pair of delicate frontal or olfactory filaments, also found in 

 forms belonging to other groups of Crustacea. Behind and hidden 

 by the labrum is the small mouth (Fig. 9). 



The posterior end of the larva is formed by a broad-based forked 

 spinous process (t), representing the thorax and abdomen of the later 

 stages. The large size of this region is a feature characteristic of the 

 Nauplii of Cirripedes. The appendages (Figs. 2, 3 and 4) as in 

 Nauplii generally, are three in number ; the antennules (Fig. 2) 

 are simple, and the antennas (Fig. 3) and mandibles (Fig. 4) 

 biramous, as usual in Nauplii. The figures show sufficiently the 

 characters of these appendages. There is in every Nauplius a per- 

 fectly definite arrangement of the various hairs, spines and other 

 processes. 



The alimentary canal shows three distinct regions : — a bent 

 oesophagus (ce.), a rounded stomach (s.), and a straight intestine (i.) 

 leading to the anus, which is situated, as in Entomostraca generally, 

 on the dorsal side of the tail ; in the Cirripede Nauplius it lies just 

 beneath the caudal spine (Fig. 9). 



The brain (Fig. 8) consists of a supra-oesophageal ganglion, on 

 which the eye rests, and from which the olfactory filaments are 

 directly given off ; behind, the brain gives off two circum-oesophageal 

 nerve cords, which unite below to form a sub-cesophageal ganglion. 



The Nauplius swims about actively and feeds and grows rapidly, 

 a definite series of moults taking place. 



A curious fact often misunderstood by naturalists is the way in 

 which, just after moulting, the various spines and hairs are at first 

 telescoped. This is a direct consequence of the mode of formation 

 of a larger organ within a smaller ; thus for the long tail to arise 

 within the cuticle of the newly hatched Nauplius, it is necessary 

 that it should become folded and telescoped within the corresponding 

 part of the younger larva : after the moult it gradually becomes 

 everted (Fig. 10). 



