498 CIRRIPEDIA. 



feet, and between the above-mentioned chitinous lamellae, the 

 cirriform feet are formed ; and on their completion the natatory 

 feet become thrown off and replaced by the permanent feet. In 

 the Lepadidae, in which the metamorphosis of the pupa stages 

 has been most fully studied, the anterior part of the body with 

 the antennae gradually grows out into an elongated stalk, into 

 which pass the ovaries, which are formed during the Cypris 

 stage. At the base of the stalk is the protuberant mouth, the 

 appendages of which soon attain a higher development than in 

 the Cypris stage. At the front part of it a large upper lip 

 becomes formed. Above the mantle and between it and the 

 shell there are formed in the Lepadidae the provisional valves of 

 the shell. These valves are chitinous, and have a fenestrated 

 structure, owing to the chitin being deposited round the margin 

 of the separate epidermis (hypodermis) cells. These valves in 

 the Lepadidae " prefigure in shape, size, and direction of growth, 

 the shelly valves to be formed under and around them" (Darwin, 

 No. 519, p. 129). 



Whatever may be the number of valves in the adult the provisional 

 valves never exceed five, viz. the two scuta, the two terga and the carina. 

 They are relatively far smaller than the permanent valves and are therefore 

 separated by considerable membranous intervals. They are often preserved 

 for a long time on the permanent calcareous valves. In the Balanidas 

 the embryonic valves are membranous and do not overlap, but do not 

 present the peculiar fenestrated structure of the primordial valves of the 

 Lepadidas. 



In connection with the moult of the pupa skin, and the 

 conversion of the pupa into the adult form, a remarkable change 

 in the position takes place. The pupa lies with the ventral side 

 parallel to and adjoining the surface of attachment, while the 

 long axis of the body of the young Cirriped is placed nearly at 

 right angles to the surface of attachment. This change is 

 connected with the ecdyses of the antennary apodemes (;/), 

 which leave a deep bay on the ventral surface behind the 

 peduncle. The chitinous skin of the Cirriped passes round 

 the head of this bay, but on the moult of the pupa skin 

 taking place becomes stretched out, owing to the posterior 

 part of the larva bending dorsalwards. It is this flexure which 

 causes the change in the position of the larva. 



