70 
THE VOYAGE OF H.M.S. CHALLENGER. 
the arms of Cephalopods as cephalic structures, interpret the nervous system, and 
especially the brachial ganglia of the animals. We will now examine the value of this 
interpretation. 
From the point of view of these zoologists, which was briefly stated above, it is 
evident : — 
1. That the union of each brachial ganglion to the corresponding pedal ganglia is a 
secondary disposition. 
2. That the cerebro-brachial connective must be a primitive structure, since it would 
represent the means by which the brachial ganglion would remain in connection with 
the cerebral ganglion from which it arose. 
We will now consider each of these conclusions separately. 
1. If, instead of regarding the nervous system of the Decapod Dibranchiates such as 
Sepiola and Ommatostrephes, which, so far as the present question is concerned, form the 
end of the series, we refer to the nervous system of the Octopoda, we shall find that in 
Octopus the brachial ganglia are only separated from the pedal ganglia by a very slight 
external constriction ; and in Cirroteuthis, which in certain respects (notably in the 
presence of fins) is a more primitive Octopod than Octopus, the brachial ganglia are in 
such close contact that the nerves to the funnel (which in Octopus arise from the pedal 
ganglia) have their origin quite close to that of the nerves to the ventral arms 1 (which 
in Octopus spring from the brachial ganglia). 
And if, in addition to what has been stated above, we do not confine ourselves to a 
macroscopic examination of the exterior of the nervous system of the Cephalopoda, but 
study it also, as I have done, by serial microscopic sections, we shall find that in Octopus 
the central substance formed by the prolongations of the cells and giving origin to the 
nerves is quite continuous between the pedal and brachial ganglia. 
If now we pass to the Decapoda and study not only the adults but also the embryos 
in all stages of development (in Sepia for example), we shall see that in the youngest 
forms the central substance of the pedal and brachial ganglia is in free communication, 
and that it is only little by little, in the subsequent stages, that they become separated 
as in the adult, where their central masses only communicate by a very slender bridge. 2 
From this point of view then, the Decapod central nervous system passes in the 
course of its development through an Octopod stage. These facts show clearly that the 
brachial ganglion results from the transverse segmentation of the pedal ganglion, and 
consequently that the union of each brachial ganglion with the corresponding pedal 
ganglion is not a secondary disposition. 3 
1 Reinhardt og Prosch, Om Sciadephorus Miilleri, K. dansk Vidensk. SelsJc. Afhandl., t. v. p. 19, pi. v. fig. 2. 
2 Stieda, Untersuchungen fiber den Bau der Cephalopoden, Zeitschr. f. vnss. Zool., Bd. xxiv. pi. xiii. fig. 6. 
3 This subject will be treated at greater length and with illustrations in a paper which I propose to publish in the 
Arch. d. Biol., t. viii., under the following title, — “Sur la valeur morphologique des bras des C4phalopodes et sur la 
composition de leur systfeme nerveux central.” 
