408 THE VOYAGE OF H.M.S. CHALLENGER. 
a summary of the researches of his predecessors, though he states that he has himself 
made some observations on Antedon rosacea at the Zoological Station at Trieste. It was 
perhaps not to be expected that he should have done otherwise than propagate the 
orthodox German view respecting the nervous system. But the account which he gives 
of the position in 1883 of the doctrine that the axial cords are nerves, is an extremely 
inadequate one. He states (p. 283) that it has been proved to be incorrect by Greetf; 
while a few pages further on (p. 290) he says that attempts have been made to support 
it by the supposition (Annahme) that fine branches proceed from the axial cords to the 
muscles and arm-segments—“ Ludwig und Greeff wiesen jedoch das Unzuliinglche und 
Unrichtige der von Carpenter angefiihrten Argumente nach.” He then refers to the 
experiments performed by Dr. Carpenter, and leaves the question for further investiga- 
tion. 
Now, in the first place, the only comment which Greeff has made upon the doctrine 
that the axial cords are nerves has been a simple denial of its truth, without any attempt 
to discuss the subject at all;! and yet this denial is referred to by Weinberg as a proof 
of the doctrine being incorrect ! 
Ludwig, on the other hand, admits that the experimental evidence seems to afford 
very considerable support to Dr. Carpenter’s views ;” but he declines to accept them on 
account of the morphological difficulties which they involve. He has been unable to find 
the muscular branches from the axial cords which have been described by Dr. Carpenter 
and myself, and more recently by Perrier, Marshall, and Jickeli. But this does not 
justify Weinberg in stating that Ludwig has proved the arguments advanced by Dr. 
Carpenter and myself to be insufficient and incorrect; nor that the existence of these 
branches is merely a supposition. The fact that they were overlooked, not only by 
Teuscher and Greeff, but also by Ludwig and Weinberg, even after I had specially 
called attention to them, is no proof of their non-existence. Two figures of arm- 
sections, showing these branches, together with a further discussion of the whole 
question, were published in my paper’ On the Minute Anatomy of the Brachiate 
Echinoderms, which appeared two years before Weinberg wrote his résumé, but is not 
referred to by him at all. 
Another point of considerable interest in its bearings on this question is left entirely 
unnoticed by Weinberg, though it was fully explained in a paper* which he quotes, and 
it was illustrated by a diagram which also shows the branches of the axial cords ; although, 
according to Weinberg, the existence of these branches is a mere supposition. I refer to 
the frequent absence of the ambulacral nerve on more or fewer of the arms of Actino- 
metra. Weinberg admits its absence on the oral pinnules of Antedon, for this was 
1 Ueber den Bau der Crinoideen, Sitzwngsb. d. Ge8ellsch. 2. Beford. d. gesammt. Naturwiss. zu Marburg, Nro. 1, 
1876, pp. 21, 22. 
2 Crinoideen, loc. cit., p. 335. 3 Quart. Journ. Mier. Sci., 1881, vol. xxi., N. S., pp. 188-192. 
4 Remarks on the Anatomy of the Arms of the Crinoids, part ii., Journ. Anat. and Phys., vol. xi., 1876, pp. 90-93. 
