1867.] Nerve Structure and Force. 155 



But as the higher manifestations of the mind become developed, 

 so we notice that the accumulation of nerve-matter about the 

 head increases ; and that moreover there is a distinct line of 

 demarcation between one kind of nerve substance, which is white, 

 and another, which is grey ; in other words, between the " nerve 

 generators," or holders, and the " nerve conductors." 



In the present communication my object will be to trace the 

 relation between the habits of the animal and the functions per- 

 formed by its different organs, with the apparent object of its 

 mission. Such an inquiry, embracing the most comprehensive field of 

 natural history, appears to me to exceed, in our day, the capabilities 

 of a single individual ; and my remarks must therefore be received 

 only as a partial contribution towards our knowledge on the subject. 



In both water and air, the two atmospheres which support 

 animal and vegetable life, nature has provided means for maintaining 

 purity and freshness. The antagonistic influences of animal and 

 vegetable respiration have long been recognized, and similar provi- 

 sions are made for fresh and salt water. The great sources of 

 impurity in the two latter would proceed from the surface and from 

 the deep, and not from the intermediate strata. On the former, and 

 especially in warm climates, we should find hosts of insect forms ; 

 in the latter, multitudes of infusoria, small Crustacea, and other 

 denizens of the water. 



It is said that if the young gnat were not devoured by fish, 

 water-fowl, &c, the air would become darkened, even in this cold 

 climate, by their immense multitudes. The same remark applies 

 with greater force to the mosquito, each female of which lays 

 annually, on the surface of water, about 300,000 ova. But there are 

 yet other forms, more minute and microscopic, which in summer 

 time may be detected in the spray thrown up by the paddle of the 

 steamboat. What means are provided for keeping within bounds 

 this exuberance of life ? 



Among the most beautiful appearances presented by the ocean 

 is the silvery phosphorescent light, seen on a summer's night, 

 illuminating the track of every boat and defining the contour of 

 the waves. This subject has been studied by many naturalists, the 

 foremost of whom is M. de Quatrefages, of Paris, whose researches 

 on Noctiluca miliaris are too well known to require comment ; and 

 an important addition to our knowledge has also emanated from the 

 labours of Professor Huxley. This luminosity proceeds in the 

 main from living invertebrate animals — Protozoa, Medusae, annelids, 

 crustaceans. Among these the most important part is played by a 

 singular and anomalous creature, of very simple organization, the 

 Noctiluca miliaris just named. This form has been described as a 

 gelatinous transparent body, about _jl of an inch in diameter, having 

 very nearly the form of a peach ; where the stalk of the peach 



