40 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



larvae escape through a hole in the sac, find another crab, and enter 

 the latter after undergoing extraordinary transformation processes. 

 The life history of Sacculhia carcini Thompson was fully described 

 and illustrated by Delage in 1884, and Delage's account has been veri- 

 fied, at least in part, by G. Smith (1906) and Veillet (1945)- It still 

 remains as the authentic history of a Saccnlina, and the following 

 story of the life and metamorphosis of this parasite is based on the 

 papers by Delage and Smith, with illustrations taken from both. 



The nauplius of Saccnlina (fig. 16 A) has the characteristic frontal 

 horns (fh) of cirriped nauplii, but it lacks an alimentary canal and 

 has neither a mouth nor an anus. After several moults the naupHus 

 becomes a cypris larva (B) with a length of 0.20 mm. On leaving 



Fig. 15. — Cirripedia: Rhizocephala. External parasitic stages on crabs. 

 A, Loxothylacus texanus Boschma, a sacculinid on Callinectes sapidus Rath- 

 bun. B, Thompsonia on Thalamita prymna (Herbst) (from Potts, 1915)- 



the brood sac on the crab, the cypris leads a free life in the ocean for 

 several days. Finally, on finding a young crab that has just moulted, 

 it attaches itself to the latter by one of its antennules (C, lAnt) , which 

 are provided with small suction cups. The point of attachment is 

 usually in the membrane at the base of a hair (Hr). When firmly 

 secured the cypris begins violent swinging movements of the body, 

 which detach the thorax (TJi) along with the legs and the abdomen 

 and throw the whole rear part of the body out of the shell (Sh). 

 From the large hole thus left in the head end of the cypris are now 

 expelled most of the internal tissues, leaving only a mass of cells con- 

 taining the reproductive elements. Later the hole closes. 



While this process of elimination has been going on, other changes 

 take place. The body of the larva separates from the shell (D) and 

 contracts to a sac walled by the ectoderm, which is much smaller than 



