340 E. RAY LANRESTER. 



they to do with the appendages and proces§es seen in other 

 Rotatoria ? In the calcar or antenna of many Rotifers 

 (double in Melicerta) "we have an organ which has always 

 suggested a comparison with an Arthropodous appendage, 

 its representative is obvious enough in Pedalion, whilst the 

 ' chin' placed opposite to it ventrally is known in other 

 forms, and sometimes regarded as a part of the trochal disc, 

 though it does not elsewhere attain the special development 

 and the musculature seen in Pedalion. The movable spines 

 of Polyarthra and Triarthra present us wdth the only 

 aj)proach which is made to anything like the other movable 

 appendages of Pedalion, and they differ essentially from the 

 latter in not being hollow processes in which the muscles 

 run, but simply pegs worked by muscles attached to their 

 inserted bases. The two small and two large pairs of arms 

 in the male of Asplanclma Sieboldii are approximations to 

 the development of true hollow limbs, but they are not pro- 

 vided with muscles. They are stated merely to shorten 

 during the swimming of the animal. It appears that, w'ith 

 the exception of the calcar, there is no structure in any 

 other Rotatoria with which any of the limbs of Pedalion can 

 be distinctly identified. If Pedalion represents, in its limbs, 

 a condition Avhich was at one time common to the Rotatorial 

 stock, the subsequent modification has, indeed, been a very 

 profound one, for not even in the embryonic condition of any 

 Rotifers are traces of such limbs to be detected. 



On the other hand, when Ave attempt to compare the appen- 

 dages of Pedalion, one by one, Avith those of a Crustacean 

 larva, Ave are met by equal difficulty. You cannot, tAvist how 

 you Avill, make out of the girdle of limbs surrounding the 

 conical body of Pedalion, an individual correspondence with 

 the laterally paired, ventrally placed limbs of Nauplius. The 

 medianly placed ventral ' chin,' and great plumed limb, and 

 dorsal antenna, and dorsal limb, seem to defy attempts at 

 tracing any such homogeny. And yet Pedalion certainly 

 Avould seem to connect the Rotatoria more closely than is at 

 present admitted AAdth the Arthropods. This connection 

 may, perhaps, be conceived of in the folloAving Avay. The 

 Rotatoria, though classed by Prof. Leydig Avith the Crus- 

 tacea, Avere shoAvn twenty years ago by Prof. Huxley (Avhilst 

 insisting on the identity of their cilio-vascular system Avith 

 that of the Annuloida) to possess in their ciliated trochal 

 disc an organ Avhich could justly be compared to the ciUated 

 bands presented by certain Echinoderm, Gephyrean, and 

 Annelid larva?. It seems to me to be equally true that this 

 same organ is represented in the velum or ' Segel ' of larval 



