98 APHRODITACEiE. 



retractile proboscis, and feet to every ring of the body, armed with 

 spines (aciciiU), bristles {festucce) more or less retractile, and with 

 soft appendages highly developed, but in no instance wdth the 

 crotchets (uncvmli) which belong to less typical orders. In form, 

 the JphroditacecB are in general very unlike the majority of Anne- 

 lides, 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 Aphroditaceos 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 cutaneous or epidermoid layers ap- 

 plied the one against the other, but capable of being separated so as 

 to become vesicular, 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 defective in this 

 respect, and of the feet which follow, the alternate 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 alter- 

 nation 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 alterna- 

 tion of squamous and naked feet prevails throughout the whole 

 length of the body, as in the genus Acoete ; and in the Palmyra 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 lamellse, 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 Phyllo- 

 doce being all alike. No other Annelide offers any similar structure ; 

 so that the presence of feet garnished with scales which alternate 

 with other feet destitute of that appendage, is unquestionably one of 

 the most important characters of the present family, and its leading 

 peculiarity. 



The elytra are very variable in number, and their shape is not 

 always alike. From their structure it appears probable that they 

 are subservient to respiration, yet we see them often associated with 

 organs to which the name of branchise has been given. These are 

 concealed below the elytra, and have the form of small crests or 

 cutaneous nipples ; they occupy the upper part of the base of the 

 feet, and are always placed within and above the cirrus of the dorsal 

 branch. Sometimes these little appendages are scarcely visible, and 

 they are very rarely to be detected on the squamigerous feet, — that 

 is, on the feet of the second, the fourth, the fifth, the seventh, the 



