ANNELIDES. 85 



a comparison of them with the stigmata of insects, and they have 

 been even mistaken for true respiratory spiracles ; but it would be 

 more correct to compare them with the hooked bristles that garnish 

 the prolegs of caterpillars, and are subservient to progressive motion. 

 In most Annelides the feet are essentially the same in structure 

 throughout the body. In those which have hooked bristles, the 

 feet furnished with them are found only on a certain portion of the 

 segments, and the feet of the other rings are armed with bristles 

 properly so called. 



6. Cirri. — The cirri have often the form of long subulate fleshy ten- 

 tacles (No. VIII. figs. 3, 4, 5, e,f)y but sometimes they are No. IX. 

 merely small compressed leaflets or papillary tubercles. 

 In general they are partially contractile ; and some have 

 a ringed or moniliform appearance. The cirri of the 

 anterior segments, in which the feet are obsolete or 

 wanting, are, as has been already mentioned, called 

 tentacular cirri, or simply tentacula. The anal seg- 

 ment is equally apodous, and the cirri which issue from 

 its end are named styles (No. IX. fig. 6, a). 



The proper cirri are usually two to each foot, originating near the 

 base of each branch, and hence they are distinguished into the 

 superior (figs. 3, 4, 5, e) and the inferior cirrus (/). The cirrus 

 may arise, however, from the apex of the dorsal branch ; and there 

 are Annelides in which so many as seven pairs are to be counted on 

 a single ring ; but in these instances they represent all the other 

 fleshy appendages. The cirri are almost always absent in the Anne- 

 lides whose feet are coronated with hooked bristles ; and also from 

 those whose feet consist merely of a few bristles without any pro- 

 tuberant papillary base. 



7. Branchice. — The structure of the organs so designated permits, 

 in some instances, no doubt to be entertained as to the functions 

 they are destined to fulfil. Such is the case when the organ is in 

 the form of a little crimson arbuscle, or in tufts or fan-shaped crests 

 (fig. 9) ; but when it is a simple or a pectinated filament (No. X. 

 figs. 7 & 8), or a nipple-like lobe, or merely a membranous tubercle, 

 there is no organic character to distinguish them from cirri, and their 

 function is less decided * . In number and position the branchiae are as 

 variable as in their figure, and they are placed either on the head, or 

 along the back, or along the sides, or at the tail. M. de Quatrefages 

 arrives at the following conclusions as to the respiration of the Anne- 

 lides : — " 1 . Respiration general and entirely cutaneous (^Lumbri- 

 conereis). — 2. Respiration cutaneous, but confined to certain seg- 

 ments {Ch(jetopterus) . — 3. Respiration cutaneous, but confined to 

 certain points of each segment (Nereis). — 4. Respiratory organ 

 taking the form of a simple caecum or bladder into which the blood 



♦ It is true in general that the appendages of the anterior rings tend to take 

 a dorsal position, and those of the posterior rings a ventral position. The 

 branchiae are always superior to the other appendages of the foot, or dorsad ; and, 

 in doubtful cases, the nature of the organ may be presumed from the position it 

 occupies. 



