10 HISTORY OF CRUSTACEA. CHAP. II. 



unusual among the Amphipoda, and the structure of 

 the clasp-forceps differs so much from what is seen else- 

 where in this order, and agrees so closely in the five 

 species, that one must unhesitatingly regard them as 

 having sprung from common ancestors belonging to 

 them alone among known species. But one of these 

 species, M. Fresnelii, discovered by Savigny, in Egypt, 

 is said to want the secondary flagellum of the anterior 

 antennse, which occurs in the others. From the trust- 

 worthiness of all Savigny's works there can scarcely be 

 a doubt as to the correctness of this statement. Now, 

 if the presence or absence of the secondary flagellum 

 possessed the significance of a distinctive generic cha- 

 racter, which is usually ascribed to it, or if there were 

 other important differences between Melita Fresnelii 

 and the other species above-mentioned, which would 

 make it seem natural to separate M. Fresnelii as a dis- 

 tinct genus, and to leave the others united with the 

 rest of the species of Melita that is to say, in the 

 sense of the Darwinian theory, if we assume that all 

 the other Metitse possessed common ancestors, which 

 were not at the same time the ancestors of M. Fres- 

 nelii this would stand in contradiction to the conclu- 

 sion, derived from the structure of the clasp-forceps, 

 that If. Fresnelii and the four other species above-men- 

 tioned possessed common ancestors, which were not also 

 the ancestors of the remaining species of Melita. It 

 would follow 



