REMARKS ON PEDALION. 339 



Proceeding from before backwards^ we find below the 

 mouth a median ^novable process bearing long vibratile cilia, 

 which Dr. Hudson speaks of as the ciliated ' chin.' Cor- 

 responding to this dorsally is the appendage bearing 

 motionless setse at its apex, which is frequently present 

 in rotatoria, and is S]3oken of as ' calcar,' ' siphon/ ' ten- 

 taculum/ or ' antenna,' sometimes being double. This 

 appendage in Pedalion is moved by two transversely-striated 

 muscular fibres. Immediately below the chin, in the median 

 line ventrally, we have the great ventral limb, by far the 

 largest of the series. It has a broad base extending almost 

 across the whole width of the Pedalion's trunk, and is con- 

 siderably longer than that portion of the animal, reaching 

 out behind when not used for lashing the water. It tapers 

 posteriorly, and ends in an expanded plume of eight com- 

 pound hairs. Corresponding to this, on the dorsal surface, 

 is a similar median limb, smaller in size and furnished with 

 fewer hairs. The two pairs of lateral appendages arise from 

 nearly the same level, or zone, as do the large ventral and 

 smaller dorsal limbs. The more dorsally placed limbs of 

 each of these lateral pairs correspond to] one another, and, in 

 like manner, the two more ventrally placed agree. They all 

 terminate in a plume similar to that of the great ventral 

 limb, which they resemble with this difference that they are 

 very much shorter. It is impossible to deny to these appen- 

 dages the title of ' limbs,' in the sense in which it is aj^plied 

 to the movable appendages of Crustacea. The disposition 

 of the muscles within them, and their vigorous movements, 

 warrant us in considering them as structures of a nature 

 identical with that of the appendages of such a crustacean 

 as the Nauplius-form. Yet there is no evidence in these 

 limbs of the chitinization of the integument in segments so 

 as to form distinct joints. It is clear that the base, or inser- 

 tion, in all the appendages of Pedalion acts as a joint, since 

 they are seen to bend at this part ; also the large ventral 

 limb and its smaller dorsal fellow are seen to bend at a 

 second point, about midway between the origin and apex. 

 The strongly marked character of the striated muscular 

 tissue by which these appendages are worked, and the nature 

 of the hair-like productions of the chitinous integument at 

 their terminations, go far to justify their assimilation to a 

 larval Crustacean's limbs, the secondary processes on the hairs 

 being peculiarly suggestive of such affinities. 



If it be admitted, then, that the appendages of Pedalion do 

 stand in some close relationship to those of Crustacean larvse, 

 what are we to suppose that relationship to be ? and what have 



