134 MR. CYRIL CROSSLAXD OX THE [June 16, 



finds in his specimen of this species from Naples that^ the setae 

 described by Clapar^de as " incompletement composees " end m a 

 simple hook covered by a guard*, whereas in the 'Porcupine' 

 specimen a second hook is present a short distance behind the 

 terminal one. Also in the former the gill is borne on the foiirth 

 foot, in the latter on the fifth, and in both cases, simultaneously 

 with its appearance, the ventral cirrus is thickened and shortened, 

 presenting an intermediate stage between the normal pointed 

 organ of the first feet and the secretory pad which represents it 

 throughout the remainder of the body. This consensus in the 

 variation of three characters seems a suflicient ground for the 

 separation of the specimens as two distinct varieties. 



The question, however, now arises as to whether these characters 

 always vary together and in the same direction, or whether their 

 variations may not occur independently and sporadically. 



As regards the difference between the set?e, Claparede men- 

 tions the occasional appearance of a second hook. Both in 

 Prof. Mcintosh's specimens and in my own we find that the 

 young setfe which do not yet project from the foot are always 

 provided with the second tooth, which in my Naples specimens 

 may be present or absent in those setfe which are exposed. This 

 indicates that, in spite of the absence of a scar in some cases and 

 the unbroken condition of the guard in nearly all, the lack of the 

 proximal tooth is always accidental, and is owing to its brittleness 

 and to the flexibility of the delicate guard. In the Zanzibar 

 specimens a distinct scar is always to be seen in those rare cases 

 where the somewhat stouter hook has been lost. 



In three specimens from Naples the first gill was borne on the 

 fourth, in three others on the fifth foot, the total number of gills 

 varying between 37 and 50. Out of nine examples from Zanzibar 

 only two bear their first gill on the fifth foot, and the total 

 number is between 46 and 59. The first gill is usually about half 

 the length of the largest, but in two cases those borne by the 

 fourth feet were only a quai'ter of that length. In the three 

 Naples specimens, the fourth feet of which are devoid of gills, the 

 same appendages bear hooked setfe and ventral cirri of the normal 

 form ; but in the three other examples, the fourth feet of which 

 possess gills, they bear simple setee and possess ventral cirri which 

 are knob-like in form. Of nine Zanzibar specimens, in five cases 

 the change in the ventral cirrus takes place on the first, being 

 deferred to the second branchiferous foot only in the remaining 

 two, and in one of these cases the foot on which this change 

 occurs is the sixth. Though I have not found a case of the 

 extension of the hooked setfe to the first gill-bearing foot in any 

 of the Naples specimens, I find such setfe to be present on these 

 feet in all those from Zanzibar, even in the two cases where this 

 is the fifth foot. 



* As in the lower riglit-liand seta of tliose figured by Claparede. His other figures, 

 as noted above, are optical delusions. See Prof. Mcintosh's note on the ' Porcupine ' 

 specimen in the ' Annals and Magazine of Nat. History,' loe. cit. 



