Page:Proceedings of the Royal Society of London Vol 69.djvu/32

24 One fact, however, must be borne in mind. It has been assumed throughout that the vertebra and nerves of any given segment in one specimen are homologous Avith the vertebra and nerves of the segment with the same serial number in another specimen. In other words, to quote Bateson ( (4), p. 32), " it has been assumed that the individuality of each member of the meristic series is respected." How far such a proceeding is justifiable is open to question. All that can be urged in support of it is, that firstly, we have been dealing with members of the same species all through, and secondly, that if the assumption is made, the variations under consideration no longer appear as a mass of dis- jointed facts, but group themselves with a certain coherence as the results of a process going on in this region of the body, a process of which we do not understand the cause, but to which has been given the term of limb-migration.

The facts recorded in this paper may be summarised as follows : (1.) Considerable variation occurs in Amnthia-s inilpuris with re- gard to

(.) The serial number of the girdle-piercing nerves.

(/>.) The number of the post-girdle nerves.

(c.) The number of nerves forming the collector.

(d.) The number and position of the nerve canals.

(<?.) The number of the fin rays.

(/.) The number of the whole vertebrae.

(2.) Asymmetry occurred in an appreciable number of cases.

(3.) Differences occurred in the two sexes on the following points. The position of the girdle was more rostral in the male than in the female. The post-girdle fin innervation area is greater in the male than in the female, owing to the development of the mixipterygium.

(4.) The female is on the whole more variable than the male.

(5.) A well-marked correlation exists between

(a.) The position of the girdle and the number of collector nerves. (b.) The position of the girdle and the number of post-girdle nerves.

(c.) The position of the girdle and the number of whole vertebras.

(6.) No correlation was found between the number of the fin rays and the number of fin nerves.

(7.) At certain stages in ontogeny the number of collector nerves is greater than in the adult.

(8.) At certain stages in ontogeny the number of post-girdle nerves is greater than in the adult. The most caudal two or three of these form a posterior collector a structure which is never found in the adult