333 



lamina cribrosa, and is perforated by the escaping bundles of 

 nerve-fibres. I am unable to offer you any account of its 

 functions. Before the ciliary muscle was known, it was for- 

 merly thought to be the foctor of accommodation, against 

 which, however, is the absence of muscularity. H. Miiller 

 suggested that it may subserve the nutrition of the vitreous 

 humour in the absence of a retinal vascular system. But 

 there are very large eyes with correspondingly bulky vitreous 

 humour and no retinal vascular system, without j)ectens, and 

 this throws doubt on Miiller's suggestion. 



Although reaching its maximum development in birds, the 

 pecten is not restricted to them. It is present in lizards. In 

 the gecko, iguano and chameleon it is a little sword-like 

 process, having an intricate structure identical with that of 

 the bird's jjecten, but externally unlike this in its surface 

 being smooth and not plaited. Some snakes also have a 

 pecten. I have found it in the boa constrictor and viper, but 

 it is absent from the common snake. 



On Sl'ONTA^'EOUs Generation and Evolution. 



By W. T. Thiselton Dyer, B.A. 



Professor of Botany, Royal College of Science, Dublin. 



The value of a theory must be measured not only by 

 the number of known facts which it correlates and explains, 

 but chiefly also by its capacity for adding to actual know- 

 ledge in giving new turns to investigation. Whatever may 

 be the different estimates of the modern philosophy of evolu- 

 tion from the first point of view, no one can doubt that it has 

 supplied an immense stimulus to research in often unsuspected 

 fields, Avhile old ones have been reattached by the help of 

 new ideas and Avith no less advantage. 



Among other inquiries which evolution has more or less 

 directly encouraged, it is not surprising to find the problem 

 of the de novo production of living things. As long as 

 spontaneous generation simply served the purpose of con- 

 cealing ignorance as to the development and reproduction of 

 many of the higher organisms/ it was natural that it 



^ "Eveu as late as 1854 we find Ton Siebold stating that he had arrived at 

 the decided conclusion that intestinal worms do not originate by "equivocal 

 generation" from substances of a dissimilar nature — namely, ill-digested 



VOL. X. NEW SER. Z 



