412 CIRRIPEDIA. 



By the free Cypris stage, into which the larva next passes, a very 

 complete metamorphosis has been effected. The median and paired 

 eyes are present as before, but the dorsal shield has become a bivalve 

 shell, the two valves of which are united along their dorsal, anterior, 

 and posterior margins. The two valves are further kept in place by 

 an adductor muscle situated close below the mouth. Remains of the 

 lateral horns still persist. The anterior antennae have undergone the 

 metamorphosis already indicated. They are four-jointed, the two 

 basal joints being long, and the second provided with a suctorial disc, 

 in the centre of which is the opening of the duct of the so-called 

 antennary or cement gland, which is a granular mass lying on the 

 ventral side of the anterior region of the body. The gland arises 

 (Willemoes Suhm) during the Nauplius stage in the large upper lip. 

 The two distal joints of the antennae are short, and the last of them 

 is provided with olfactory hairs. The great upper lip and second 

 pair of antennas and mandibles have disappeared, but a small papilla, 

 forming the commencement of the adult mandibles, is perhaps de- 

 veloped in the base of the Nauplius mandibles. The first pair of 

 maxillae have become small papillae and the second pair probably 

 remain. The six posterior pairs of appendages have grown out as 

 functional biramous swimming feet, which can project beyond the 

 shell and are used in the locomotion of the larva. They are composed 

 of two basal joints, and two rami with swimming hairs, each two- 

 jointed. These feet resemble Copepod feet, and form the main ground 

 for the views of Glaus and others that the Copepoda and Cirripedia 

 are closely related. They are regarded by Glaus as representing the 

 five pairs of natatory feet of Copepoda, and the generative appen- 

 dages of the segment behind these. Between the natatory feet are 

 delicate chitinous lamellae, in the spaces between which the cirriform 

 feet of the adult become developed. The ventral spinous process 

 of the Nauplius stage is much reduced, though usually three-jointed. 

 It becomes completely aborted after the larva is fixed. 



In addition to the antennary gland there is present, near the dorsal 

 side of the body above the natatory feet, a peculiar paired glandular 

 mass, the origin of which has not been clearly made out, but which is 

 perhaps equivalent to the entomostracan shell gland. It probably 

 supplies the material for the shell in succeeding stages 1 . 



The free Cypris stage is not of long duration ; and during it the 

 larva does not take food. It is succeeded by a stage known as the pupa 

 stage (fig. 232 B), in which the larva becomes fixed, while underneath 

 the larval skin the adult structures are developed. This stage fully 

 deserves its name, since it is a quiescent stage during which no nutri- 

 ment is taken. The attachment takes place by the sucker of the 



1 There is considerable confusion about the shell gland and antennary gland. In 

 my account Willemoes Suhm has been followed. Glaus however regards what I have 

 called the anteunary gland as the shell gland, and states that it does not open into the 

 antennae till a later period. He does not clearly describe its opening, nor the organ 

 which I have called the shell gland. 



