NO. 10 



CRUSTACEAN METAMORPHOSES — SNODGRASS 



39 



the body only around the ends of the muscle. The peduncle of the 

 stalked barnacles is a product of the head and becomes occupied by 

 connective tissue and muscles. The barnacles are hermaphroditic, but 

 they generally live in crowded colonies and cross fertilization is made 

 possible by a long, tubular penis arising at the base of the vestigial 

 abdomen. 



The Rhisocephala. — In this suborder of parasitic cirripeds we en- 

 counter the strangest metamorphic phenomena known in the whole 



Fig. 14. — Cirripedia: Thoracica. (A-E from Runnstrom, 1924-1925.) 

 A, Balanus balanoides (L.), nauplius. B, same, anterior end of body with 

 median eye and frontal horns {fh). C, same, cypris larva. D, same, later stage, 

 barnacle plates formed inside cypris shell. E, same, first antenna of cypris with 

 attachment cup on third segment. F, Balanus ebnrneus Gould, group of adults. 

 G, Lepas anserifera L., adult animal in natural position removed from shell. 

 H, same, stalked shell. 



animal kingdom. The rhizocephalans include a number of genera, of 

 which the best known are crab parasites of the genus Sacciilitui. The 

 visible external evidence that a crab is parasitized by a sacculinid is 

 the presence of a large saclike body attached ventrally on the crab at 

 the base of the abdomen (fig. 15 A). This external sac is the re- 

 productive part of the parasite containing the ovaries and the testes, 

 but from it long, rootlike processes extend into the body of the crab 

 and serve for the nutrition of the parasite. The eggs are fertilized 

 and hatch within the external sac, giving rise to nauplii, which trans- 

 form into typical cirriped cypris larvae. The free-swimming cypris 



