38 report— 1877. 



in the water, and some species are found some miles inland. Their short 

 antennae differ from those of the truly aquatic genera of the Lysianassidce, 

 and are evidently organs in a rudimentary condition, impoverished in charac- 

 ter and small, because they have no duties to perform. In the Ilyperidce they 

 have also assumed an impoverished condition probably from a similar cause, 

 although the habits of the creature are very distinct. In the Orchesticlce and 

 Oniseidce the animals live out of what might be pronounced to be their 

 accustomed element ; whereas in the Ilyperidce they are inhabitants of tho 

 sea, but exist if not parasitic, certainly encased within Medusae in such a 

 way as to lose much power of free action. Organs of sense, such as the 

 anterior antennae are generally considered to be, must lose their power 

 from want of use, owing, in the one case, to altered conditions, and in the 

 other to incapacity for action. 



Talitrus and Hyperia arc generally considered by carcinologists to rank 

 at opposite extremities of the order ; and when generalization is adopted 

 from too narrow observation, a faulty conclusion is liable to be enunciated, 

 such as that which identifies a short antenna as typical of an improved 

 organization on the one hand, or as evidence of a more feeble typo on 

 the other. 



Among tho Entomostracous forms of Crustacea the first pair of antennae 

 correlates with various forms, and apparently loses its functional sense. In 

 Nebalia it varies so little from the normal form, that it must be admitted as 

 part of the evidence that this genus ranks higher in the natural order of 

 Crustacea than the Entomostraca. In Limnadia these appendage appear 

 to have degenerated into a. simple flagcllum, the peduncle or stalk having 

 become impoverished to the same extent. In Daphnia they appear to be 

 wanting. In Cypris they are Hagelliform and robust. In Pontia they 

 are fiagelliform and long, and they are very long in Cychjis. In Caligvlidce 

 they are reduced in size and feeble in form, and frequently support organs 

 of adhesion of sucker-like appearance. In the Lerneans and close allies 

 they are wanting, unless, as is probable, they homologize with the organs 

 of insertion, in which case correlation is carried to an extreme elcgrce. 



The object or function of this pair of antennae has by all the older carcino- 

 logists been supposed to fulfil the duties of an olfactory organ. Dr. Farrc, 

 in the ' Philosophical Transactions' for 1843, was the first who attempted to 

 reverse this decision. In 1S51 Professor Huxley communicated to the 

 ' Annals of Natural History,' 2nd ser. vol. vii. p. 304, some " Zoological Notes 

 and Observations made on board H.M.8. ' Rattlesnake ' during the years 

 1840-51. I. On the Auditory Organs of Crustacea." He says that " The older 

 authors, Fabricius, Scarpa, Brandt, and Trcviranus, unanimously confer the 

 title of auditory organs on certain sacs filled with fluid which arc seated in 

 the basal joint of the second or larger pair of antennae ;" but " by the 

 majority of the older writers no notice is taken of the sac existing in 

 many genera in the bases of the first or smaller pair of antenna?. Rosen- 

 thal *, however, describes this structure very carefully in Astaeus flaviatilis 

 and Astaeus (Paliiiurus) marinus. He considers it to be an olfactory organ, 

 while he agrees with previous writers in considering the sac in the outer 

 antennae as the auditory organ." 



This view is supported by Professor Milne-Edwards, as I shall show when 

 writing about the second pair of antennae. 



This distinguished carcinologist appears to have given no consideration to 

 * "Ueber Gerucbsorgane cl. Insekten," Keifs Arcliiv, Bd. x. (1811). 



