REPORT ON THE ANNELIDA. 
33 
that the two former organs escaped the notice of MM. Audouin and Milne-Edwards, in 
their original description of the species from Port Jackson, where it was obtained by 
Capt. Freycinet in his celebrated voyage round the world. In two instances in the British 
Museum the specimens occurred amongst barnacles. 
Family Aphroditidjs. 
The descriptions of the family given by Kinberg and other authors render it 
unnecessary to define it on the present occasion. All the genera procured in the 
Expedition of the Challenger fall under those already described, yet there are some forms 
which, from their intermediate structure, help to clear up the relationshi]3s between 
Aphrodita, Lcetmonice, and Hermione, and especially indicate the steps between the two 
first mentioned. Something of the same kind, however, is brought to light without 
traversing the great oceans^ viz., in watching the development of the bristles in the 
ventral branch of Hermione hystrix. 
Those authors who, like Savigny, Milne-Edwards, De Quatrefages, Grube, and Ehlers 
place the Aphroditidse, Polynoidse, Acoetidse, and Sigalionidse in one family have certain 
grounds for this step. Thus all have biramous segments, all have ventral cirri on every 
foot; the scales are borne by similar segments ; the head has two eyes on each side, a 
median tentacle, a pair of palpi, and four tentacular cirri. Moreover, there is a certain 
agreement in regard to the arrangement and relation of the great nerve-cords, which in 
Aphrodita occur in a transversely elongated space between the ventral attachments of 
the oblique muscles, bounded externally by the hypodermic basement-tissue of the 
cuticle ; in Polynoe they occupy a hypodermic area between the ventral longitudinal 
muscles, the oblique muscles piercing the vertical at the upper and outer angle of the 
space, and being attached externally and superiorly to the cords. In the Acoetidse they 
are situated in the hypodermic region between the ventral longitudinal muscles (which 
are closer than in the Polynoidse), a thin layer of the former occurring between them 
and the cuticle. The great oblique muscles pass down do their upper and outer border. 
Lastly, in the Sigalionidse the space between the ventral longitudinal muscles is still 
more narrowed than in the previous group, and the hypodermic area for the nerves is 
thus increased in depth. Superiorly the arch is completely covered by the insertions of 
the vertical and oblique muscles; and the latter do not pierce the former (which occupy the 
middle line), but are attached to the basement-tissue below them on each side of the 
nerve-area. It will be observed that there is a gradational narrowing of the ventral 
longitudinal muscles between the first and last mentioned groups. 
On the other hand there are fair reasons why several authors adhere to the anmigement 
of these groups in separate families. Thus, for instance, the Polynoidse diverge 
(zOOL. CHALL. EXP. PART XXXIV. 1885.) LI 5 
