ON OUR PRESENT KNOWLEDGE OF THE CRUSTACEA. 41 



perly for them, and should not be led to require as ' the thing ' a lot of other 

 information involving greater trouble and higher fees to the limitation of 

 general reference to the chemist. The sooner the public learns that chemists 

 do not want to take advantage of them, but only to do what is of use to them, 

 and that fees are not to be regulated by the number of items given (any more 

 than an amount of money by the number of coins of various values it may be 

 paid in, but also by the intrinsic value of each), the better I think it will be." 



In the foregoing Eeport the Committee has attempted to give an epitome of 

 the very voluminous replies which have been received. 



It will be perceived that there are many points on which the evidence is 

 very conflicting ; and the Committee feels it impossible to recommend with 

 confidence any particular process or processes unless the special conditions of 

 accuracy are very clearly defined. 



The large amount of infoi-mation amassed during the past year has indi- 

 cated very distinctly the directions in which further research is desirable ; and 

 the Committee, if reappointed, will be able to complete the proposed experi- 

 ments and inqviiries before the next Meeting of the Association, and make a 

 full report on the whole subject it was appointed to investigate. 



Report on the Present State of onr Knowledge of the Crustacea. — 



Part I. On the Homologies of the Dermal Skeleton. By C. Spence 



Bate, F.R.S. ^c. 



[Plates I. & II.] 



In presenting a Report on the present state of our knowledge of the Crustacea, 

 I do not think that I should fulfil the object in view without drawing atten- 

 tion to what must be one of the greatest hindrances to the progress of any 

 study in an exact or scientific manner. I allude to the want of a uniformity 

 in scientific nomenclature. 



The names of the several groups and families, as well as those of the struc- 

 ture of the animals, given by the earHest carcinologists, having been based on 

 a limited knowledge both of the forms and the variation to which this great 

 subkingdom is liable, make them inapplicable to the knowledge of the period. 

 Leach named one great group of Crustacea Decapoda, from the number of 

 legs that it possesses ; and Dana more recently named another group Tetra- 

 decapoda, from the fourteen legs that belongs to its most normal forms. 



Observation has demonstrated that in this latter group some genera, as 

 Anceus, have but eight legs ; while in the Decapoda it is only a conventional 

 rule that prevents the genus Palmnon and its allies from having the appendages 

 of the percion anterior to the last five pairs counted as legs. 



But a greater difiiculty still exists where the names given to any parts of 

 the animal carry any significance with them that precludes their being ac- 

 cepted in their universally correct sense. Thus the third pair of maxUlipedcs 

 in the Brachyurous Crustacea are identical with the first pair of walking-legs 

 in the Stomapoda, Amphipoda, and most of the Isopoda. 



It is now exactly twenty years (1855) since I presented to the Association a 

 Report on the British Edriophthalmia, in which the same difficulty was pointed 



