24 Mr. R C. Punnett. On the Composition and Variations 



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. 

 (/'.) 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 



