(119 ) 
VII.—On Some Points in the Early Development of Motor Nerve Trunks and 
Myotomes in Lepidosiren paradoxa (Fitz.). By J. Graham Kerr, Regius 
Professor of Zoology in the University of Glasgow. (With Six Plates.) 
(Read January 18 ; MS. received February 9, 1904. Issued separately July 1, 1904.) 
CONTENTS. 
PAGE PAGE 
INTRODUCTORY . : : ; : : 119 | GeneRaL Remarks ; ; , : 5 125 
DEVELOPMENT OF THE Motor Nerve Trunks . 119 | ExpLanation oF PiLateEs , _ ; , 127 
DEVELOPMENT OF THE MYoMERES . : s 122 
INTRODUCTORY. 
My main purpose in the following short paper is to publish figures illustrating some 
of the more important facts of the early development of myotomes and motor nerves 
in Lepidosiren. The bearing of some of the observations of nerve development upon 
current theories renders it particularly desirable that they should be illustrated by 
- untouched photographs of the sections. A few photographs illustrating the more 
important stages*™ in the development of the motor nerve trunks are given on Plate I. 
For the preparation of the photographs here published, as well as several others, I am 
indebted to the skill of my friend Dr T. H. Brycn, and of Mr Finexanp, our University 
photographer. 
DEVELOPMENT OF THE Moror TRUNKS OF THE SPINAL NERVES. 
In describing the observed phenomena it will be convenient to begin with a late 
stage in development and work backwards to the earlier stages, and so pass from the 
better known and more familiar to the less known and less familiar. 
Stage 34.—Fig. 1 illustrates a considerable length of motor. nerve from stage 34.t 
Here the nerve (n.t.) consists of a cylindrical mass of nerve fibres about 13 in 
diameter. On the surface of this the nuclei of the protoplasmic sheath are conspicuous. 
The greater part of the sheath itself is so thin as to be mvisible even under the 3 mm. 
immersion objective, except in the neighbourhood of each nucleus, where it swells out 
to form a thick mass containing the nucleus. 
Stage 31.—At this stage the nerve rudiment on superficial examination presents 
the appearance simply of a chain of nuclei placed end to end in a strand of protoplasm. 
* By stage n I mean the stage represented by fig. n in my paper on the external features during development, 
Phil. Trans. Roy. Soc. B., vol. excii. p. 299. 
+ Cf. Rarrartr’s fig. in Anat. Anz.,1900, p. 340 (Per la genesi dei nervi da catene cellulari). Cf. also KOLLIKER’s 
remarks on this, op. cit., p. 511. 
TRANS. ROY. SOC. EDIN., VOL. XLI. PART I. (NO. 7). 20 
