Dr. Johnston on the British Aphroditacece. 425 



the body, armed with spines (aciculi), bristles {festucce) more 

 or less retractile, and with soft appendages highly developed, 

 but in no instance with the crotchets (uncinuli) which belong 

 to less typical orders. In form the Aphroditacece are in ge- 

 neral very unlike the majority of Annelides, for the body in 

 most of them is short, flattened, and more or less inclined to 

 oval, although there are among them some which are slender, 

 elongated, and nearly as cylindrical as the Nereides. But there 

 is nothing more remarkable in the external structure of the 

 generality of the Aphroditacece than the large membranous 

 scales or elytra, as Savigny calls them, which lie along the 

 back in a double series and cover it like a coat of mail. These 

 organs are affixed to the base of the superior branch of the 

 feet by means of a short pedicle, and are formed of two cu- 

 taneous or epidermoid layers applied the one against the 

 other, but capable of being separated so as to become vesi- 

 cular, and at certain seasons of the year they appear to be 

 filled with ova. There are, however, in all Aphroditacece a 

 certain number of feet which carry no scales or elytra, and 

 which alternate with those that are provided with them. The 

 first, the third, and the sixth pairs are almost constantly de^ 

 fective in this respect, and of the feet which follow, the alter- 

 nate pairs for a more or less considerable extent of the body ; 

 but after the twenty-third, the twenty-fifth, or the twenty- 

 seventh segment this regular alternation ceases, for posterior 

 to one or other of these segments the feet may be either all 

 squamous or all entirely naked, or the elytra may continue to 

 appear and disappear alternately, but in an altered series ; for 

 it is now not every other but every third foot which bears an 

 elytron. Instances, however, occur in which the binary alter- 

 nation of squamous and naked feet prevails throughout the 

 whole length of the body, as in the genus Acoete ; and in the 

 Palmyre of Savigny there are no elytra at all. 



In some of the Nereides (Phyllodoce) we find on each side 

 of the body a series of foliaceous lamellae which resemble the 

 scales of the Aphroditacece, but these are really very different 

 organs, and never disposed in the alternating manner of the 

 latter, the feet of Phyllodoce being all alike. No other Anne- 

 lide offers any similar structure, so that the presence of feet 



