18 CIRRIPKDIA, 



in the aborted antennae, the rudimentary eyes, and in the 

 minute parasitic males (when such exist), there is a more 

 direct relation to the Suctorial division of the Entomostraca; 

 but some of these resemblances are probably only analogical, 

 resulting from the fixed condition of both groups. It should 

 not be overlooked, that out of the three orders into which 

 Cirripedes may be divided, in the two latter, the mature 

 animal presents hardly any resemblance to an Entomostra- 

 can. From the distinct presence in either pupa or mature 

 animal of the fourteen segments of the cephalo-thorax; from 

 the apparent composition of the carapace, as will be subse- 

 quently explained ; and from the concentrated condition of 

 the nervous system, one is led to glance at the higher Crus- 

 tacea; and here we shall find amongst the Podophthalmia,one 

 aberrant group of low organisation, namely, that including 

 Phyllosoma, Amphion, &c, in which more points of resem- 

 blance to Cirripedes may be detected, than, as I believe, in 

 any other group whatever ; for we here see that remarkable 

 elongation of the head in front of the mouth, so eminently 

 characteristic of Cirripedes; we have a carapace overlapping 

 the thorax, which is sometimes free beneath ; we have the 

 abdomen sometimes almost obsolete ; we have biramous 

 legs : and especially we have the posterior cephalic and the 

 first thoracic appendages more or less rudimentary and ob- 

 solete ; and this, I infer from Mr. Dana, is a very rare phe- 

 nomenon, though characteristic of all ordinary Cirripedes, in 

 which the seventh and eighth segments with their appen- 

 dages have disappeared. In the order including Phyllo- 

 soma, &c, namely, in the Macroura, the ganglions which 

 give nerves to the five posterior thoracic limbs, are distinct 

 from the great sub-cesophageal ganglion which supplies 

 the several anterior appendages ; this is the case with those 

 Cirripedes in which all the infra-cesophageal ganglions 

 are not concentrated into one. In the Macroura and 

 Brachyoura, the first pair of legs almost always differs 

 in structure from the others, so does the homologous r 

 second cirrus in Cirripedes differ from the four succeeding 

 pairs ; in some few Macroura, the second leg is antenni- 

 ibrmed, so in some few cases is the homologous (or third) 

 cirrus; J. Vaughan Thompson was even struck by the 



