152 A REPORT ON THE SIPUNCULOIDEA, COLLECTED BY DR WILLEY 



The two largest collections of Sipunculoidea, that of Professor Semper, and that 

 of Dr Sluiter, which have been worked out, were collected in the seas surrounding 

 the Malay Archipelago and the Philippine Islands. This probably accounts for the fact 

 that in Dr Willey's collections I have found no new species, and it must also be taken 

 into account in assigning the headquarters of certain genera to these seas. But making 

 due allowance for the fact that these seas have been more carefully searched than mam- 

 other parts of the globe, it still seems to me that this region is the centre of the 

 above-mentioned genera of Sipunculoidea. 



Sipunculus priapuloides has a curious distribution, being found off the Norwegian 

 coast, and again at the Loyalty Islands. 



The determination of the species of a Sipunculid is not always an easy matter. 

 Some are readily enough identified and the task is rendered easier if the animal dies 

 with its head extended. But this is seldom the case and then it is not easy to make 

 out the arrangement of the tentacular crown, the number of tentacles etc. 



In those species which are provided with hooks the number of rings in which they 

 are usually arranged and the shape of the hooks are of systematic value, but here 

 again we are met with the difficulty that the hooks are often worn away with age 

 and it is not possible to tell how many rings have disappeared. Further, the shape and 

 size of the hooks are by no means constant, but vary considerably in the same species 

 and even in the same specimen. 



Again the number of longitudinal muscles in those species in which this muscular 

 coat is split up into bundles is an important specific character, yet in many species 

 the bundles anastomose to such an extent, that the number of bundles at any one level 

 differs from that at any other. This fusing and splitting of the bundles also obscures 

 the question of the exact origin of the retractor muscles. 



Perhaps one of the most fruitful sources of difficulty is the difference of colour 

 and the relative prominence of the papillae which is brought about by the varying 

 states of contraction in which the animals die. The pigment of the skin is as a rule 

 aggregated around the mouths of the papillae, and when the animal is killed in a 

 contracted state, the colour is much deeper and the papillae far more prominent than 

 when the skin is relaxed. Hence as in the case of Gloeosiphon aspergillum for example, 

 specimens are met with whose appearance is so different that at first sight one is 

 disposed to think that at least two distinct species exist, but a more minute observation 

 tends to show that the superficial differences depend largely on the condition in which 

 the creature died. 



Species are a matter of opinion and few groups of animals afford so wide a range 

 for divergency of opinion as do the Sipunculoidea. 



It should be mentioned that all the specimens examined had been long in spirit 

 and were killed with diverse reagents. This may to some extent account for the very 

 different appearance and colour presented by some specimens of the same specif-. 



