2OO 



THE CRUSTACEA 



only in the adult female suggest its possible homology with the 

 oostegites of the following somites. 



As an example of extreme modification of the mouth-parts and 

 of exceptionally marked changes taking place during development, 



E. . m. 



m. 



FIG. 121. 



Gnathia maxillaris. A, late larval form (Praniza-stage). B, head of same, from below, 

 further enlarged. C, adult female. D, second thoracic appendage of same, further enlarged. 

 E, adult male. F, maxilliped (first thoracic appendage) of same, further enlarged. G, second 

 thoracic appendage of same, m, mandible of male ; mxp, maxilliped of larva; II, III, VII, 

 second, third, and seventh thoracic appendages (the eighth is undeveloped in adults of this 

 family). (After Sars ; B partly after G. Smith.) 



the oral apparatus of the very aberrant Gnathia may be here 

 described. In the larval state (Fig. 121, A), Gnathia is parasitic 

 on fish, and the suctorial mouth -parts form a short conical 

 proboscis (Fig. 121, B). The mandibles are styliform, finely 

 serrate on the inner edge, without palp, molar process, Jacinia 

 mobilis, or spines. The maxillulae and maxillae are simple, slender 



