44 REPORT — 1855. 



enabled to state the circumstance from actual observation, we wish not to say- 

 much on the subject. 



We have noticed a young limb commencing at the coxa as in the higher 

 order, a circumstance which maivcs us infer that the reproduction of a lost 

 member is always from tiiat joint; and since it is necessary, before the com- 

 pletion of the new part, that the old one should be got rid of, it is thrown off 

 at the period of moulting. 



To meet with one of these animals with the limb undergoing the process 

 of redevelopment is of very rare occurrence ; so rare, that after having 

 watched some thousands in glass tanks, we remember only having observed 

 a single specimen which had two legs in this state. 



On the auditory organs. — The upper antennae are in Crustacea without 

 doubt organs of hearing of a more or less imperfect nature. This, we think, 

 has been argued to demonstration : first, by Dr. Farre, in the Philosophical 

 Transactions for 184'3, who reversed the decision of older authors, and gave 

 satisfactory reasons for considering them as auditory organs in Macroura. 

 This has been followed up by Mr. Huxley, who, in a paper in the ' Annals of 

 Natural History ' for the year 1831, supported the opinion of Dr. Farre by 

 researches on some small es-otic Macroura, and identified a "strongly refract- 

 ing otolithe" in the anterior antennae. And lately, in a paper communicated 

 to the Fellows of the Linnean Society, and published in the ' Annals of 

 Natural History' for July 1855, we have demonstrated a more elaborate 

 and higher kind of organ in the basal joint of the same antenna in the Bru' 

 chyura. 



We may here therefore take for granted, since M. Milne-Edwards' 

 * Histoire des Sciences Naturelles' was published in IS^O, in which he 

 argues these to be olfactory organs, that the present state of our know- 

 ledge accepts the interpretation of the later observations on the subject*. 

 Admitting this to be the fact, it is for us here merely to compare the 

 upper antenna of the Amphipoda with the internal of the Macroura. 



In Amphipoda the structure of the anterior antenna is very simple, and is 

 generally long and slender. The second filament, which in the higher orders 

 is commonly of equal length with the first, is in this order reduced to a rudi- 

 mentary condition, or entirely wanting. When this antenna is reduced in 

 length, it generally is increased in bulk at the base of the peduncle, as if the 

 internal organization became more important with external decreasing exten- 

 sion. Examples of this are to be found in the genus Lysianassa (PI. XHI. 

 fig. 1) and Anonyx. 



A marked exception to this is perceptible in the true Orchestia, where 

 the organ is short and unimportant, approximating towards a rudimentary 

 condition of the whole. This is a valuable fact, since it evidently is the 

 result of certain altered circumstances which interfere with the proper 

 development of the organ, which in Amphipoda generally is adapted for 

 aquatic existence only. 



Talitrus and Orchestia are in an intermediate position, their habits are 

 between the aquatic and the land Crustacea, and are the nearest approach to 

 terrestiial Amphipoda that we know. As their habits, so are their organs 

 adapted. Tlie Crustacea, which are purely terrestrial, possess no upper an- 

 tennae ; those which are semiterrestrial possess them in but a rudimentary con- 

 dition. They differ from the short upper antennze of aquatic Crustacea, such 

 as the Lysianassidce, They are evidently impoverished organs, that is small, 

 because they are not required ; they ceased to grow from an arrest of pro- 



* Von Siebold, in his recent ' Comparative Anatomy,' supports the opinion of Edwards, but 

 we think not from his own actual researches so much as from the works of others. 



