1865.] The Development of Nerve-fibres. 265 



tially of the same nature ; and it would indeed be very difficult to dis- 

 tinguish a collection of spherical masses of germinal matter, from which 

 the tissues of a new being are to be evolved, from a mass of young pus- 

 corpuscles, which may result from the rapid multiplication of masses of 

 germinal matter existing in any tissue of man or the higher animals. In 

 both cases the matter is formless; and however much the conclusion may 

 be opposed to the affirmations of great authorities, we are compelled, by a 

 review of the facts ascertained by observation, to infer that there is a far 

 greater difference in the power than there is in the chemical characters, 

 or physical properties, of the matter taking part in these changes. 



Many very interesting and highly important facts relating to this in- 

 quiry may be obtained from a careful study of the minute changes which 

 occur in the development of the tissues of the imago or perfect insect 

 during the chrysalis stage. So far as I am able to ascertain, the larval 

 tissues and organs are in the first instance completely removed, the ger- 

 minal matter increases considerably in quantity, and at length a collection 

 of new masses of germinal matter results, which take part in the formation 

 of the new tissues of the developing imago. If those who so confidently 

 affirm that all the phenomena of living beings are physical and chemical 

 would investigate some of these marvellous changes, I venture to think 

 they would very soon withdraw their confident assertions, and admit that 

 the construction of tissues and organs is a process not to be explained by 

 physics and chemistry, or accounted for by any of the known laws of 

 ordinary lifeless matter or force. 



I must now advert to a question which I feel incompetent to grapple with, 

 though I cannot permit myself to pass it over. Let me consider if, in the 

 development of new muscular fibres, nerves, and vessels, as occurs in the 

 case of the nerve-tufts of the frog, or in the development of a new ganglion 

 connected with the sympathetic, there are certain masses of germinal 

 matter which, as the direct descendants of pre-existing masses in muscles, 

 nerves, vessels, &c., take part in the development of these tissues respec- 

 tively, or if they all result from changes occurring in what would be called 

 by some a mass of undiiferentiated blastema ? In studying the early deve- 

 lopmental changes taking place in the embryo, one discovers nothing which 

 would justify the inference that one set of masses is concerned in the de- 

 velopment of all the future muscles of the body, another of all the vessels, 

 another of all the nerves, another of all the glandular organs, and so on, 

 each of these masses or collections being gradually prolonged to distant 

 parts ; but it seems rather that the whole is in the first instance formless, 

 and that the process of formation gradually proceeds in many parts at the 

 same time. The brain is not formed first, and other parts of the nervous 

 system extended from this central organ ; but the active nervous system, 

 central and peripheral, is developed as a whole, stage succeeding stage, until 

 it attains its fully developed condition in all its parts. If masses of germinal 

 matter for the development of the respective tissues were first formed, and 



