4G A HISTORY OF RECENT CRUSTACEA 



or devoted to other purposes. They may be partially or 

 entirely branchial. Among the Stalk-eyed Crustacea they 

 are often used in the female for retaining the eggs during 

 an early period of development or hatching. In the 

 Amphipoda the fourth and fifth pairs are more or less 

 adapted for springing, and bear the name of uropods, or 

 tail-feet. This name is also given to the appendages of 

 the twentieth segment whenever they are present. These 

 are prominent features in the Cumacea and most other 

 Edriophthalma, and in the Macrura they combine with the 

 telson to form the powerful tail-fan, for which Mr. Spence 

 Bate has proposed the Greek name rhipidura ("see Plate X.). 

 In the Copepoda there is a ' caudal furca,' homologous with 

 the caudal rami in the Nebaliidse, which must be distin- 

 guished from the terminal uropods of the higher Crustacea, 

 as ' being not true limbs, but more properly representing a 

 bipartite terminal segment.' ' 



21. The telson is extremely variable in form and 

 relative size, and sometimes by coalescence with the pre- 

 ceding segment shows little trace of independent exist- 

 ence. The intestinal canal opens on its under side. It 

 is sometimes deeply cleft, as though the two terga, or 

 dorsal plates, of a body-ring had come apart. To prove 

 its claim to be regarded as a segment, the most effective 

 argument would be to show that it sometimes carries 

 appendages after the fashion of all the other segments. 

 Bell, in the ' British Stalk-eyed Crustacea,' says that he 

 has frequently observed appendages to the telson of tlie 

 common prawn, Leander serratus (Pennant), ' in the form 

 of extremely minute points attached to the very extremity 

 of the segment, and moveable.' Spence Bate says, 'In 

 some genera, or even families, the telson is posteriorly 

 rounded, as in the Astacidse ; in others it is anteriorly 

 hard and calcareous, and posteriorly soft and membranous, 

 as in the Synaxidea, a circumstance that is suggestive of 

 a distinct relationship of the two parts, the anterior 

 which carries the anus belonging to the normal somite, 



' Sars. Report on the Phyllooarida aoWtalsA by H.M.S. Challmger, 

 p. 33. 



