REPORT ON THE PYCNOGONIDA. 115 



become thinner and thinner, the ganglia smaller, and the lateral branches arising 

 from the ganglia more numerous and much thinner and shorter. This is quite in cor- 

 respondence with the number of muscles which these ganglia innei-vate ; whereas 

 these in the front part of the proboscis are stouter, and separated by distinct longitu- 

 dinal intervals, in the posterior part they are thinner, and placed almost in an uninter- 

 rupted row. 



This brings us quite methodically to the function of these ganglionic nerve-bundles. 

 In the vertebrates we can distinguish by the microscopical structure sympathetic ganglia 

 and nerves from those of the cerebro-spinal system, but in the invertebrata this is by 

 no means so easy. In the first place, we must consider the function of the part of the 

 nervous system in question. The ganglia and the nerves of my three ganglionic 

 bundles innervate the striped muscles of the proboscis. Unstriped muscular fibres 

 are by no means rare in the muscular tissue of Pycnogonids,^ but even if they 

 were quite wanting, as they seem to be in the muscular tissue of the Crayfish,' those of 

 the proboscis ought to be considered as voluntary fibres. Moreover, the action which 

 the food undergoes in the proboscis by means of these fibres is of a purely mechanical 

 nature. Chemical action does not take place in it, therefore comparison of these 

 o-angliouic bundles with the sympathetic system of higher animals is impossible. 



The morphological explanation of their presence is by no means so easily given. The 

 following reasoning must be considered as an attempt only. The proboscis of the Pycno- 

 gonida in the form in which it presents itself should not, of course, be considered as a new 

 organ, only present in this class of Arthropoda. It is only an organ or a combination of 

 organs under a new form, modified under the influence of surrounding conditions. Con- 

 sidering for a moment the supposition right, that it results from the union of three parts, 

 an azygous one placed partly alcove and partly before the mouth (the upper lip), 

 and two others placed below and Ijehind the mouth, the manducating parts of the 

 mandibles, of which the palpi in that case may be considered as the feelers ; then we 

 have in the three nerves, the first of which is given ofi" by the supra-cesophageal ganglion, 

 and the two others arising from the first thoracic ganglion, the normal nerves for the 

 innervation of these parts. With the union of these parts to form a proboscis) and I 

 believe this argument will hold good also if we prefer another homology for these parts), 

 and the predominance of the manducating function of this proboscis, evidently quite a 

 new part of the nervous system, will make its appearance ; and it is not difiicult to 

 imagine its probable origin. . 



In the chitinous wall which lines the canal of the proboscis, and which is furnished 

 with rows of very numerous teeth and spines, we have, no doubt (morphologically), a con- 

 tinuation of the integument, so that its inner surface corresponds with the outer surface of 

 the body, while its outer surface, to which the muscles are attached, is the homologue 



1 E.g., in the wall of the vasa efferentia of the males, &c. * Huxley, The Crayfish, p. 181. 



