230 MANUAL OF ZOOLOGY. 



first a " Nauplius, " with an unsegmented pyriform body, a 

 median eye, and a dorsal shield or buckler. The abdomen is 

 produced beneath the anus into a long forked caudal appen- 

 dage, and there is a long spine over the anus. A mouth, intes- 

 tine, and vent are present. After several moults the young 

 Nauplii become "pupae" (fig. 85). The dorsal shield is folded 

 so as to form a bivalve shell ; the anterior limbs (antennae) 

 are transformed into prehensile organs ; the two following 

 pairs of limbs are cast off; and six pair of strong, biramose, 

 natatory feet are developed upon the abdomen. A pair of 

 composite eyes are present, but there is no mouth. Finally, the 

 pupae fix themselves by the prehensile antennae to rocks, drift- 

 wood, ships, Sponges, Cetaceans, Turtles, Crustaceans, or even 



Fig. 85. Locomotive "pupa" of Balanns. a Eye; /' Caudal bristles ; 

 c Setigerous limb?. 



Jelly-fish. The prehensile antennae are glued down perma- 

 nently by the secretion of a peculiar cement-gland. The cara- 

 pace becomes, as a rule, the seat of definite calcifications, by 

 which it is converted into a multivalve calcareous " test ; " the 

 mouth is developed, and the six pairs of natatory feet are con- 

 verted into long jointed " cirri," by which food is conveyed to 

 the mouth. " The 'cement-ducts' can be traced as far as the 

 third or ' disc-segment ' of the antennae. There the cement 

 seems to transude and fasten down the disc ; soon both an- 

 tennae are surrounded by a common border of cement, which 

 gradually increases in extent after the metamorphosis. In the 

 Lepas fascicularis the cement is poured forth in sufficient 

 quantities to form, itself, the substance to which the peduncle 

 of the adult barnacle adheres, and for a cluster of which bar- 

 nacles it constitutes a central vesicular float" (Owen). The 

 cement-gland, as shown by Darwin, is " part of, and continu- 

 ous with, the branching ovaria," and the cement-ducts open 

 through the prehensile antennae. 



The form of the adult, as already said, differs consider- 

 ably, but the two most important types are those presented 

 respectively by the Sessile and by the Pedunculated Cirri- 

 pedia. 



