4.0 HISTORY OF CRUSTACEA. Chap. VI. 



The sole unimportant exception which I have hitherto 

 met with is presented by the genus Brachyscelus,^ in 

 which the heart possesses only two pairs of fissures, as it 

 extends forward only into the second body-segment, and 

 is destitute of the pair of fissures situated in this 

 segment in other forms.^ 



without the pressure of a glass cover. Considering the common opinion 

 as to the distribution of the Amphipoda, namely, that they increase in 

 multiplicity towards the poles, and diminish towards the equator, it 

 may seem strange that I speak of a considerable number of species on 

 a subtropical coast. I therefore remark that in a few months and 

 without examining any depths inaccessible from the shore, I obtained 

 38 different species, of which 34 are new, which, with the previously 

 known species (principally described by Dana) gives 60 Brazilian 

 Amphipoda, whilst Kröyer in his ' Grönlands Amfipoder ' was ac- 

 quainted with only 28 species, including 2 Ljemodipoda, from the 

 Arctic Seas, although these had been investigated by a far greater 

 number of Naturalists. 



2 According to Milne-Edwards' arrangement the females of this genus 

 would belong to the " Hyperines ordinaires " and the previously un- 

 known males to the ' ' Hyperines anormales," the distinguishing charac- 

 ter of which, namely the curiously zigzagged inferior antennae, is only a 

 sexual peculiarity of the male animals. In systematising from single 

 dead specimens, as to the sex, age, &c. of which nothing is known, similar 

 errors are unavoidable. Thus, in order to give another example of very 

 recent date, a celebrated Ichthyologist, Bleeker, has lately distinguished 

 two groups of the Cyprinodontes as follows : some, the Cyiariuodontini, 

 have a " pinna analis non elongata," and the others, the Aplocheilini, 

 a " pinna analis elongata " : according to this the female of a little 

 fish which is very abundant here would belong to the first, and the 

 male to the second group. Such mistakes, as already stated, are 

 unavoidable by the " dry-skin " philosopher, and therefore excusable ; 

 but they nevertheless prove in how random a fashion the present 

 systematic zoology frequently goes on, without princij)les or sure 

 foundations, and how much it is in want of the infallible touchstone 

 for the value of the different characters, which Darwin's theory promises 

 to furnish. 



2 I find, in Milne-Edwards' ' Le9ons sur la Physiol, et I'Anat. comp.' 

 iii. p. 197, the statement that, according to Frey and Leuckart, the 

 heart of Caprella linearis possesses five pairs of fissures. I have ex- 



