264 



ZOOLOGY FOR MEDICAL STUDENTS 



CHAP. 



The CiRRiPEDiA are a group of Crustacea which have entirely given 

 up the free-living existence^ being attached to rocks, to floating objects, 

 or to the bodies of other animals, and in correlation with this the bodily 

 structure is greatly modified in the adult — although here again there is 

 a typical nauplius larval stage (Fig. no. A). The nauplius swims about 

 and after a few days ecdysis takes place accompanied by a considerable 

 change in form. It is now (Fig. no, B) known as a " Cypris '' larva — 

 from its resemblance to the members of the group Ostracoda (p. 266) : 

 its body is enclosed in a bivalve carapace, and there are six pairs of 



Fig. 1 10. 

 Nauplius (A) and Cypris (B) stage? of Sacculina. x about 70. (From Geoffrey Smith in Tht 

 Cambridge Natural History, vol. iv.) A.i and Ant, First antenna; A. 2, sec.nd antenna; Ab, 

 abdomen; E, undifferentiated cells; F, horu-like projection ; G, glands; H, tendon ; M, mandible ; 

 T, tentacles. 



Y-shaped thoracic legs by the movements of which it swims. The first 

 antenna carries a flattened disc upon which opens the duct of a cement 

 gland producing a sticky secretion. When the Cypris larva swims 

 up against a solid object it is apt to adhere to it and it may be observed 

 apparently strugghng to free itself, making as it were several steps with 

 its sticky antennae, until at last its attempts cease and it remains fixed 

 in position. The cirripede now gradually takes on its adult form. It 

 remains attached to the solid object by its head end : the boldy is 

 enclosed in a carapace-like fold of skin termed the mantle ; the compound 

 eyes disappear and the six pairs of swimming legs are replaced by much 



