CIRRIPEDIA. 289 



In a subsequent memoir*, Mr. Thompson described and figured 

 larvae of the Lepas and Cineras. The young Lepas, at the stage at 

 which it was observed, somewhat resembles the entomostracous genus 

 Cyclops {^fig. 127). It has a single median sessile eye-speck, three 

 pairs of members, the most anterior of which are simple, the others 

 bifid. The back of the animal is covered, like the Argulus armiger, 

 by an ample shield, terminating anteriorly in two extended horns, and 

 posteriorly in a simple elongated spinous process. 



The discoveries of Mr. Thompson have been abundantly con- 

 firmed by Audouinf, Wagner J, Burmeister§, Goodsir||, Bates ^[, and 

 Darwin.*''" 



In a ^ew Cirripeds, e. g., the species of Cryptophialus^ the changes 

 from the <ig^ to the pupa take place within the sack of the parent. 



Fig. 127 illustrates the form of the " larva," or first stage, in both 

 pedunculated and sessile Cirripeds, at least after the second moult. 

 Before the moult, the horns, including the second antennie and the 

 caudal appendages c, are less developed ; and are always shorter in 

 Balanus than in Lepas. The general form of the larva is a de- 

 pressed oval, the body inarticulate, with a carapace covering the 

 dorsal surface. The eye (of) often appears to be due to a confluence 

 of two eyes. Behind the eye there arise a minute pair of horns, or 

 sheaths containing the rudimental antennae of the first pair. The 

 large lateral horns (^, e) contain the second pair of antennae ; they are 

 amongst the earliest developed organs, as in the larvae of the Crus- 

 tacea. The mouth is more or less proboscidiform, and is situated 

 between the first or second pairs of natatory legs ; the oesophagus 

 extends from it anteriorly, as in Limidus. The first pair of natatory 

 legs has a simple terminal joint ; the second and third pairs have 

 bifid terminal joints, or are biramous, in all the genera, as in Lepas 

 (yfig. 127). Darwin regards the natatory limbs as answering to the 

 second, third, and fourth thoracic limbs in the Crustacea. Behind 

 these limbs the trunk is produced, and terminates in a horny forked 

 appendage, which becomes much elongated, as in fig. 127, after the 

 first moult. In some larvae a second, and even a third fork, then 

 appears, indicative of an articulated abdomen. 



In the second stage of the larva the carapace is much changed : the 

 second or great antennse become prehensile organs ; the first pair 

 disappears ; the eye has become double ; but the mouth is still simply 

 suctorial, although advanced in position. The three pairs of thoracic 

 limbs retain their larval character. 



* CCXXVI t CCXXVIT. p. 31. t CCXXIX. p.467. 



§ CCXIV. II CCXXX. pi. iii. and iv. 



% CCXXVTIL pi. 6, 7, and 8. ** CCXXIII. and CCXXIV. p. 102. 



u 



