178 SUMMARY OF CURRENT RESEARCHES RELATING TO 



become seminiferous tubules in the testis, medullary cords in the ovary. 

 When they are formed, it is possible to distinguish the sexes, for the 

 number of primordial germ-cells remaining in the germinal epithelium 

 after the formation of the cords of first proliferation is small in the 

 male, and not greatly diminished in the female. 



Beginning with the eighth, but especially during the ninth, tenth, 

 and eleventh days of development, there is a rapid increase in the 

 number of primordial germ-cells in the germinal epithelium of the 

 female. Three or four dividing germ-cells may be seen in a small area. 

 Collected into groups, which are the result of successive mitoses, the 

 primordial germ-cells, or oogonia as they may now be called, give rise to 

 lobulations which appear on the deep surface of the epithelium. These 

 lobulations or buds, composed chiefly of oogonia, but including also 

 cells of peritoneal parentage, increase in size and become the cords of 

 second proliferation or cortical cords. The oogonia become definitive 

 ova, while the peritoneal cells of the germinal epithelium, present in 

 the cortical cords, develop the follicular epithelium. 



Intracranial Ganglion on Oculomotor Nerve of Dogfish.* — G. E. 

 Nicholls has observed in three specimens of iScyUimn ninicula a small 

 collection of ganglion cells associated with the oculomotor nerve. They 

 are probably of normal occurrence, and oculomotor ganglia are known 

 to be present, either as functional structures or vestiges, in widely 

 separated vertebrate types. Since ganglia, <jther than sympathetic, are 

 known to occur normally only upon " sensory nerves," or on the dorsal 

 root of mixed nerves, the question arises : What is the significance of 

 the occurrence of ganglia upon the oculomotor ? 



From the available evidence, which is somewhat indefinite and con- 

 flicting, three facts emerge : (1) that in the primordium of the oculo- 

 motor, cells are fouud derived by migration (a) from the medulla, and 

 {li) from the neural crest ; (2) that certain of these cells in the oculo- 

 motor primordium migrate into the primordium of the ciliary ganglion, 

 precisely as do cells from a typical dorsal ganglion into a typical sympa- 

 thetic ganglion ; and (3) that the weight of evidence appears to be 

 against the belief that cells of medullary origin contribute to the 

 formation of sympathetic gangha. The inference is that the cells 

 which pass along the oculomotor to the ciliary ganghon mast have been 

 derived, in the first instance, from the neural crest. 



The author seeks to estabUsh the proposition that the oculomotor is 

 not correctly viewed as the equivalent of a ventral root only. " Rather 

 we must accept it as the homologue of a complete segmental nerve, 

 containing elements of both dorsal and ventral roots, although some of 

 these components have apparently become obsolete, and the distinction 

 of the originally separate dorsal and ventral roots has disappeared." 



The occurrence in the oculomotor of afferent nerve fibres (conducting 

 centripetally impulses arising in sensorial end-organs), and of ganglion 

 cells upon the root of the nerve almost certainly related to these afferent 

 fibres, taken in conjunction with the part which this nerve plays in the 



• Proc. Roy. Soc. B., Ixxxviii. (1915) pp. 553-68 (1 fig.). 



