ORDERS OF. 21 



which the fundamental difference consists in the limbs or 

 cirri being thoracic in the first , abdominal in the second ; 

 and entirely absent in the third. For the sake of showing 

 the range of character in Cirripedes, to which allusion has 

 been made, I will briefly indicate the leading differences in 

 each order. In the Thoracica, three families are included, 

 — the Balanidas, or sessile Cirripedes, the Verrucidse, re- 

 markable from their quite asymmetrical shell, and the Lepa- 

 didse, or pedunculated Cirripedes. The great difference in 

 external appearance between these three families is known 

 to all naturalists. Even within the one family of Lepa- 

 didse there are great differences in external appearance, as 

 will be admitted on comparison of Lepas, Pollicipes, Con- 

 choderma, &c. ; but we have also important internal diffe- 

 rences, as in the case of Anelasma,in which the cirri are barely 

 articulated, and are not capable of seizing prey, whilst the 

 mouth is almost probosciformed, with the outer maxillae and 

 palpi rudimentary : still more important are the differences 

 in Alcippe, in which the cirri of the first pair act as brushes ; 

 the second, third, and fourth pairs being quite aborted ; and 

 the fifth and sixth pairs consist only of four segments, 

 with one of the two normal rami converted into a crenated, 

 button-like projection, for the sake apparently of triturating 

 food ; Alcippe, also, is very remarkable in being destitute of 

 a rectum and anus. In this same genus Alcippe, in Ibla 

 and Scalpellum, there are either separate males or Comple- 

 mental males, some of which are so utterly abnormal in 

 their characters, that by no definition which I could frame, 

 could they be included even in their proper Order, much 

 less in their proper Family. 



In the second order of Abdominalia (PI. 23 and 24) 

 the seventh or last cephalic segment is quite distinct, and 

 bears rudimentary organs, answering to the first pair of 

 maxillipeds of ordinary Crustaceans, of which organs, and of 

 the segment supporting them, there is no trace in the Tho- 

 racica : the seven succeeding thoracic segments are destitute 

 of any appendages; but the three segments of the abdomen 

 bear three pairs of cirri. The mouth is peculiar in the labrum 

 being developed into very large, moveable, lancet-formed 

 organ ; and the lower end of the oesophagus is armed with 



