2 Mr. E, C. Pimnett. On the Composition and Variations 



" On the Composition and Variations of the Pelvic Plexus in 

 Acanthias mdgaris" By E. C. PUNNETT, B.A., Gonville and 

 Cains College, Cambridge. Communicated by H. GrADOW, 

 F.E.S. Eeceived February 16, Eead March 7, 1901. 



Whilst recently engaged upon the development of the pelvic plexus 

 in Mustelus kerns I was much struck with the amount of variation in 

 the number and position of the nerves forming it. This led me at the 

 time to examine all the material which I was able to procure, and the 

 results obtained have been given in a previous paper (12, 1900). 

 Believing, however, that, in Bateson's words, " the facts of variation 

 must be the test of phylogenetic possibility " (4, p. 30), I determined 

 to examine a still larger number of specimens of some other species of 

 shark. The only two species in this country which from their abund- 

 ance lend themselves to such an investigation are Scyllium ainimla and 

 Acanthias mdgaris. The former possesses certain advantages in that it 

 would l)e possible to institute comparisons with the nearly allied 

 8. mtitlus which co-exists with it in the same locality. Such ad- 

 vantages, however, are to some extent discounted by the greater 

 difficulties which Sri/Hiu/it presents in working. Owing to the greater 

 abundance and toughness of the connective tissue it is not nearly 

 such a favourable object for investigation of this kind as Ai-nnthws. 

 This is also the case with the embryos those of Acanthias giving far 

 clearer preparations with the gold chloride method mentioned below 

 than the Scyllium embryos. The presence of a large " nervns col- 

 lector " in Acanthias also gives it an advantage over ScyUiuin where 

 the " collector " is usually represented only by a single branch. 



The research was carried on at Plymouth in the summer of 1899 

 and of 1900, whilst occupying at the Laboratory tables both from the 

 British Association and from Cambridge University. To the autho- 

 rities of the Biological Station I would express my thanks for the ample 

 supply of material forthcoming. I also take this opportunity of 

 expressing my gratitude to Dr. Gadow for the kind sympathy which he 

 has shown during the course of the work. 



The anatomy of the pelvic plexus of Acanthias vulgari* has been 

 studied by Davidoff (1) and by Brans (10). Davidoff's account may 

 be briefly summarised as follows : 



The pelvic fin is innervated by seventeen nerves whose serial 

 numbers are 3147. Of these nerves 4047 each divide on reaching 

 the fin, into a dorsal and a ventral portion which innervate respectively 

 the fin musculature lying dorsally and ventrally to the fin skeleton. 

 Before supplying the muscles, however, the ventral branches all run 

 into a longitudinal nerve, lying at right angles to their direction 



