530 Dr Willey, The Development of Peripatus, etc. [May 16, 



(3) The development of Peripatus novae-britanniae. By Dr 

 A. Willey (Balfour Student). 



The ova are without yolk and the nutrition of the embryo 

 is effected by the development of a large trophic vesicle which 

 occupies the entire dorsum of the embryo and projects far in 

 front of the embryo as a head-fold and behind as a tail-fold. The 

 trophic vesicle is thus a hollow closed cylinder lined internally by 

 endoderm and externally by ectoderm, the cells of the latter being 

 adapted for absorption of nutriment. The trophic folds were 

 compared with the amniotic folds of insects. The trophic cavit} r 

 becomes the gastral cavity of the adult and in the transformation 

 from one to the other the endoderm undergoes certain changes. 

 It secretes a basal membrane and a cuticular membrane simul- 

 taneously with a great increase in thickness ; and between the 

 two membranes the endoderm contains numerous small and 

 large yolk-like globules which are probably to be regarded as 

 reserve nutrient matter to tide the embryo over the first few 

 days of its independent life. This late deposition of reserve 

 nutrient matter derived ultimately from the maternal organism, 

 as opposed to foreign ingested matter, is probably of some 

 significance with regard to the question of the lecithality of 

 the ovum. The embryo lies outside on the ventral surface of the 

 trophic vesicle just as an insect embryo lies upon the yolk. 



(4) On the possibility of deducing magneto-optic phenomena 

 from a direct modification of an electro-dynamic energy function. 

 By Mr J. G. Leathem, M.A., St John's College. 



[Printed in the Transactions, Vol. xvn. Pt. I.] 



The method initiated by Maxwell for the explanation of the 

 Faraday effect depended on the direct insertion of a magneto- 

 optic term in the energy. This method was extended by 

 Fitzgerald and others to the explanation of Kerr's effect, namely 

 the modification introduced in the circumstances of optical 

 reflexion by magnetisation of the reflector. A difficulty occurred 

 however in satisfying all the interfacial conditions, which virtually 

 showed that such a scheme was not formally self-consistent. 

 The origin of the discrepancy has been traced by Mr Larmor 

 (Report on the Action of Magnetism on Light, Brit. Assoc. 1893) 

 to omission to secure what may for shortness be called the 

 electromotive incompressibility of the medium : in the ordinary 

 problem of optical reflexion there is no tendency for this to be 

 disturbed, but when Maxwell's magneto-optic energy terms are 

 included the reaction against compression introduces what ma}' be 

 termed an electric pressure, which must appear in the equations. 



