114 



SOME VARIATIONS in the SPIXAL NERYES of the 



FROG, with a NOTE on an ABNORMAL 



VERTEBRAL COLUMN. 



By F. J. Cole, 



University College, Liverpool. 



With Plates I. and II. 

 [Read Dec. 14, 1900]. 



The subject of variation is one which is unexpectedly 

 and often unpleasantly brought home to the mind of 

 every demonstrator of Zoology at the outset of his career. 

 As two classic instances of what Bateson calls meristic 

 variation may be cited the so-called ki spinal nerves " of 

 the Frog, and the apertures of the reproductive ducts in 

 Nephrops norvegicus. With regard to the former, it 

 happens not infrequently that the tenth or coccygeal 

 nerve is apparently absent, whereas the fact is that the 

 sciatic plexus is, as I consider, " postfixed," the tenth 

 spinal nerve shows a considerable abnormal increase in 

 bulk, and completely goes over into the Nervus 

 ischiadicus, instead of only partially doing so, or not 

 doing so at all. In these cases the seventh spinal nerve 

 does hot as a rule contribute any fibres to the sciatic 

 plexus. And with regard to Nephrops, abnormalities in 

 the oviducal and spermatic apertures are by no means 

 uncommon, and I remember examining three specimens, 

 two of which were abnormal, and had four supernumerary 

 spermatic apertures between them, occurring as follows : 

 A B 



Third walking leg • 



• • Fourth ,, • 



• • Fifth „ • • 



