126 



THE CRUSTACEA 



in Laurci (Fig. 77) is distinctly segmented into six "thoracic" and 

 three limbless " abdominal " somites, and ends in a caudal furca. 

 In Petrarca and Dendrogaster the body is unsegmented. 



In the three genera just named a pair of preoral appendages are 

 present (Fig. 77, ant) and, except in Laura, are armed with hooked 

 spines suggesting that they are organs of fixation. They differ from 

 the adhering antennules of the Thoracica and Acrothoracica in being 

 inserted, at least in Laura, at the sides of the buccal region and 

 more or less enveloped by the mantle. It is possible that they are 

 in reality the antennae, but there seems to be no definite evidence 



FIG. 76. 



Laura gerardiae. A, external view of the animal attached to a branch of the coral Gerardia 

 (soft tissues of coral removed). B, the mantle-sac split open showing the body in the middle. 

 The ramified hepatic diverticula, which are accompanied by branches of the ovary, are seen in 

 the mantle on each side. (After Lacaze-Duthiers, from Encycl. Brit.) 



on the point. The cement-glands, so characteristic of other Cirri- 

 pedia, appear to be absent. 



The mouth-parts are more or less reduced, but appear to be 

 adapted for piercing. 



The thoracic appendages are biramous and articulated only in 

 Synagoga. In Laura they are uniramous and indistinctly segmented, 

 and the first pair differs from the others, being long and slender. 

 A similar difference is observed in Petrarca, where, however, they 

 are still further reduced, and in Dendrogaster they are represented 

 only by some indistinct papillae. 



In all three genera the gut ends blindly, and the hepatic 

 diverticula (Fig. 76, B; Fig. 77, F), which are large, extend into 

 the mantle. A digastric "adductor" muscle is present on the 



