94 MICROSCOPICAL STUDIES. 



passing successively through those special phases known as the 

 Nauplius and Cypris stages. 



The most primitive type is that of the stalked or pedunculate 

 forms, and of these, Lepas is the most typical genus. The young 

 of this, emerge from the egg as very tiny Nauplii minute larva? 

 furnished with but three pairs of appendages, all used at first as 

 swimming organs (Fig. 19, PI. viii, Vol. I). The two anterior pairs 

 represent the two pairs of antennae while the third pair ultimately 

 become the mandibles in the adult. The first pair of these limbs 

 are simple ; the others are biraniosc (two-branched). One eye, 

 unpaired and median the Nauplius-eye is developed, and the body 

 is protected by a dorsal shield-shaped fold of integument, the broad 

 anterior margin produced on either side into a fronto-lateral horn. 

 Mouth, alimentary canal and anus are present, and the creature feeds 

 eagerly. Frequent moults (ecdyses) take place, and with each such 

 change, important additions are made to the number of the organs 

 and appendages ; a series of segments are produced posteriorly, 

 destined to form the adult thorax ; limbs sprout from these, and a 

 compound eye appears on either side of the Nauplius-eye. 



At last a moult occurs when a larva quite different to any of the 

 preceding Nauplius gradations issues from the old skin. In this 

 new phase the larva has the general form of an Ostracod hence is 

 called the Cypris-stage being provided with a bivalve shell, 

 composed of two oval convex valves, open along the ventral edge, 

 within which the entire body and its limbs can be retracted. All 

 three regions of the typical crustacean body, head, thorax and 

 abdomen, can be traced (Fig. 24, PL I). The thorax has six strong 

 limbs, while the abdomen, short and insignificant, possesses but a 

 single pair. Of the appendages of the head, the second pair repre- 

 senting the posterior antennae have' disappeared, while the third 

 pair are reduced from their former important biramose character to 

 small mouth organs the mandibles. Tiny swellings, that ultimately 

 become the first and second maxillae, are also to be seen. The first 

 antennae on the other hand, increase in size and become provided 

 with a bell-like sucker on the penultimate joint, and on this sucker 

 opens a cement-producing gland. The larva now ceases feeding, 

 much food reserve appearing as oil-globules, especially at the anterior 

 end of the body. 



The time has now arrived for the assumption of adult life, and 

 this is set about by the larva attaching itself preferably to some 

 floating body by means of the suckers on the first antennae. Next 

 the cement glands pour out their secretion at the same spot, and 

 embed the anterior end of the body firmly. The head region elongates, 

 becomes a mere stalk, the bivalve cypris-shells fall away, a chitinous 



