BENNETT, ON THE MOLECULAR THEORY. 51 



divides first, and that the molecules of the yolk are attracted 

 round the two centres so formed. But numerous observations 

 had satisfied the author that both spermatozoid and germinal 

 vesicles are simply dissolved among the molecules of the 

 yolk, from the substance of which, stimulated and modified 

 by the mixture so occasioned, the embryo is formed ; a view 

 which has further the merit of explaining what is known of 

 the qualities of both parents observable in the offspring. He 

 was only acquainted with one exception to this general law, 

 viz., the development of Pyrozoma, recently described by 

 Mr. Huxley, the description of which, however, was incom- 

 plete."^ The truth appears to be that, in an analogous 

 manner to that in which the pigment-molecules of the skin 

 are stimulated by the access of light to enter into certain 

 vital combinations with one another, so are the molecules of 

 the yolk stimulated by the access of the spermatozoid to pro- 

 duce those other vital combinations that result in a new 

 being. The essential action is not so much connected, as 

 has hitherto been supposed, with the cell-wall or nucleus as 

 with the molecular element of the ovum. 



With regard to nutrition — food and all assimilable mate- 

 rial must be reduced, in the first instance, to the molecular 

 form, while tlie fluid from which the blood is prepared, viz., 

 chyle, is essentially molecular. Most of the secretions origi- 

 nate in the effusion of a fluid into the gland-follicle, which 

 becomes molecular, and gives rise to cell formation. In 

 muscle, the power of contractility is inherently associated 

 with the ultimate molecules of which the fasciculus is com- 

 posed ; and lastly, the gray matter of the sensory ganglia, 

 and of the brain, which furnishes the conditions necessary for 

 the exercise of secretion, and of even intellect itself, is asso- 

 ciated Avith layers of molecules which are unquestionably 

 active in producing the various modifications of nervous force. 

 These molecules are constant and permanent as an integral 

 part of these tissues, as much as cells or fibres are essential 

 parts of others, and their function is not transitory, but es- 

 sential to the organs to which they belong. 



All these facts point to the conclusion that vital action, so 

 far from being exclusively seated in cells, is also inti- 

 mately associated with the elementary molecules of the 

 organism. 



III. This leads me, in the third place, to an enunciation 

 of the molecular law of growth, which a study of the nume- 

 rous facts previously referred to has induced me to frame, 

 viz. : — That the development and growth of organic tissues is 

 * 'Annals of Natural History,' Jan., 1860, p. 35. 



