Development and Circulation of the Myriapoda. 373 



sets of fibres, namely, an upper and an under one, communicating 

 with the cephalic ganglia ; a transverse or commissural, which com- 

 municates only with corresponding nerves on the opposite side of the 

 body ; and a lateral set, which communicates only with nerves from 

 another ganglionic enlargement on the same side of the body, and 

 which forms part of the cord in the interspace between the gan- 

 glia. The author had long suspected that this latter set of fibres 

 existed ; but he had never, until lately, ascertained their presence by 

 actual observation. Their action seems fully to account for the re- 

 flected movements of parts both anterior and posterior to an irritated 

 limb ; as that of the commissural set does the movements of parts 

 situated on the opposite side of the body to that which is irritated. 

 In the ganglia of the cord in lulus and Polydesmus, the fibres of the 

 inferior longitudinal series are enlarged and softened on entering the 

 ganglion, but are again reduced to their original size on leaving it; 

 thus appearing to illustrate the structure of ganglia in general. In 

 the developement of the ganglia and nerves in these genera, and 

 also in Geophilus, the same changes take place as those which were 

 formerly described by the author as occurring in insects ; namely, 

 an aggregation of ganglia in certain portions of the cord, and shift- 

 ing of the position of certain nerves, which at first exist at ganglionic 

 portions of the cord, but afterwards become removed to a non- 

 ganglionic portion. The nervous cord is elongated, in order that it 

 may keep pace with the growth of the body, which is periodically 

 acquiring additional segments : that this elongation takes place in 

 the ganglia is proved by these changes of position in the nerves lying 

 transversely across the ganglia. The author infers from these facts, 

 that the ganglia are centres of growth and nourishment, as well as 

 of reflex movements, and that they are analogous to the enlarge- 

 ments of the cord in the vertebrata. 



A series of experiments on the lulus and Lithobius are next re- 

 lated; the result of which shows that the two supra-oesophageal gan- 

 glia are exclusively the centres of volition, and may therefore strictly 

 be regarded as performing the functions of a brain : so that when 

 these ganglia are injured or removed, all the movements of the ani- 

 mal are of a reflex character. When, on the other hand, these gan- 

 glia are uninjured, the animal movements are voluntary, and there 

 exists sensibility to pain : there is, however, no positive evidence 

 that the power of sensation does not also reside in the other 

 ganglia. 



The second part of the paper relates to the organs of circulation. 

 In all the Myriapoda and Arachnida the dorsal vessel or heart is di- 

 vided, as in insects, into several compartments, in number corre- 

 sponding to the abdominal segments. Its anterior portion is divided, 

 immediately behind the basilar segment of the head, into three di- 

 stinct trunks. The middle portion, which is the continuation of the 

 vessel itself, passes forwards along the oesophagus, and is distributed 

 to the head itself; while the two others, passing laterally outwards 

 and downwards in an arched direction, form a vascular collar round 

 the oesophagus, beneath which they unite in a single vessel, as was 



