5 GO THE MICROSCOPE. 



Rotifera, the Tocnladce and the Nematoidea, may be con- 

 sidered as the most aberrant groups of their respective 

 series. 



Under the head Annelida, Mr. Huxley includes the 

 errant and tubicular Annelids of Cuvier, and the Gcphyrea 

 of De Quatrefages; he thinks that the Terricola — the 

 Earthworms and Naides — should be separated from the 

 Scoledce of Milne Edwards, and brought into the same 

 group. So far as external structure is concerned, the 

 genus Polynoe is, perhaps, the best fitted to serve as the 

 type to which other Annelida may be referred: the com- 

 monest form of the genus being the P. squamata. 1 The 

 best developed branchiae among the Annelids are possessed 

 by the Amphinomidce, the Ennicidce, the Terebellidce, and 

 the Serpulidce. The branchiae in the three former families 

 are ciliated, branched plumes or tufts attached to the 

 dorsal surface of more or fewer of the segments. In the 

 last they are exclusively attached to the anterior segments 

 of the body, and present the form of two large plumes, 

 each consisting of a principal stem, with many lateral 

 branches; this stem is itself supported on a kind of 

 cartilaginous skeleton. 



The teeth in a great number of the Annelida are very 

 curious and distinctive. In the Polynoe there are four, 

 planted in the muscnlar wall of the proboscis. In the 

 Nereis there are two powerful teeth working horizontally, 

 besides minute accessory denticles. In Syllis there is a 

 circle of sharp teeth, stirrounding a triangular median 

 tooth. In Glycera there are a pair of teeth ; but the most 

 complex arrangement of teeth is that presented by the 

 Ennicidce. The tubicular Annelids possess neither pro- 

 boscis nor teeth. 



Many Annelids pass through a larval condition, in 

 which the body exhibits mere indications of segments, 

 and the appendages are entirely absent; locomotive 

 function being performed by a circlet of cilia, disposed 

 around the anterior part of the body. There is a large 

 group of very remarkable organisms, observes Mr. Huxley, 

 the minute " wheel animalcules," Rotifera, whose whole 



(1) Consult a valuable paper on this genus in Miiller's Atchiv. 1857. Also 

 Huxley's " Elements of Coin] arative Anatomy." 



