1879.] On the Characters of the Pelvis in the Mammalia, §c. 395 



Neither of these two authors has referred to my statements at all, but 

 both have entirely ignored them. I am now able to repeat them, and 

 to give them much greater force. No less than twenty- three out of 

 the forty-eight species of " Challenger " Actinometrce, and three species 

 in Semper's collection, have more or fewer grooveless arms. I have 

 cut sections of these arms in two species, and have obtained the 

 same results as with Act. polymorpha and Act. Solaris. The "ventral 

 nerve" and ambulacral epithelium are conspicuous by their absence, 

 while the axial cords in the skeleton, which I also regard as true 

 nerves, give off branches freely in the centre of each arm-joint, as 

 I have already described for other species both of Actinometra and of 

 Antedon. Two points are noteworthy. In one species, one of the 

 posterior ambulacral grooves stops quite abruptly on the disk, some 

 little way from the arm bases, and the two arms to which it would 

 naturally have gone with its " nerve," tentacles, &c, receive no 

 branches from any of the adjacent grooves to supply the deficiency. 



Lastly, in the gigantic Philippine species already referred to as 

 No. 37, there are more than one hundred arms, many of which are 

 grooveless and " nerveless," as I have found by section-cutting. But 

 these abnormal arms are not limited to the posterior part of the 

 body, as is usually the case, for there are several on each radius. 



Evidence of this negative character appears to me to be a serious 

 objection to the German view that the subepithelial bands constitute 

 the only nervous apparatus of the Crinoids. Ludwig* attacks Lange's 

 opinions as to the Aslerid-nerves, on the ground that the structures 

 supposed by Lange to be nerves are not constant, but are absent from 

 the arms of certain species. It is curious, however, that Ludwig is 

 unable to apply this reasoning to his own views respecting the nerves 

 of the Crinoids ! 



III. " On the Characters of the Pelvis in the Mammalia, and. the 

 Conclusions respecting the Origin of Mammals which may 

 be based on them." By Professor Huxley, Sec. R.S., Pro- 

 fessor of Natural History in the Royal School of Mines. 

 Received February 24, 1879. 



[Plate 8.] 



In the course of the following observations upon the typical 

 characters and the modifications of the pelvis in the Mammalia, it 

 will be convenient to refer to certain straight lines, which may be 

 drawn through anatomically definable regions of the pelvis, as axes. 



* "Beitr'age zur Anatomie der Asteriden." " Zeitschr. fur Wiss. Zool.," Band 

 xxx, p. 191. 



> 2 g 2 



