72 T. C. WHITE ON THE HISTOLOGICAL DEVELOPMENT 



organs met with in an examination proceeding from the head to the 

 tail, I will say a few words on those organs which extend through 

 all the segments. 



The nervous system first demands our consideration as the main- 

 spring of this wonderful and interesting life. Taking their rise in 

 the two united ganglia which form the brain, two cords of nervous 

 matter passing from the dorsal aspect to the ventral, divide to 

 embrace the pharynx, and uniting below form the sub-cesophageal 

 ganglion, the first of a chain of ganglia which terminates in the 

 ninth segment. In its earliest stage this ventral chain, like the 

 brain, was structureless and gelatinous in its character, whilst its 

 ganglia were indicated by rude unshaped swellings. The connecting 

 cords could scarcely be described as fibrous, but soon the borders of 

 all became more defined, and nervous fibrillar could be seen dis- 

 tributed to the muscles and organs in their neighbourhood. It is 

 about this time that the muscles begin to show an opalescence when 

 viewed with a spot lens, and I call your attention to this fact because 

 of the interesting connection existing between the completion of the 

 nervous system and the commencement of histological organization ; 

 under a moderately high power and careful illumination this opales- 

 C3nce can be resolved into fine but irregular striation of the muscular 

 fasciculus, the stria3 not marshalled into the regular order character- 

 istic of the muscular fibre later on, but scattered about in i( admired 

 disorder." Entering the sarcolemma of the muscle together with the 

 nerves, are delicate branches of the tracheal system ; the growth of 

 these tubes would form a most interesting subject for future study. 

 In the early stages of development, the viscera of this larva are held 

 in position by apparently structureless ligaments which connect the 

 viscera with the interior of the body cavity ; in the later stages these 

 ligaments are perforated in their interior by the growing tracheal 

 tubes, which, terminating in exceedingly fine ends, may nevertheless 

 be seen by daily observation to be pushing their way onwards, and 

 giving off similar branches to adjacent organs, and so furthering 

 their development, because the nervous system may furnish life, but 

 the respiratory function must support it, and so the two functions 

 take place almost side by side, the nervous system getting rather 

 the start. The muscular system may be divided into three groups, 

 those which supply the jaws, those confined to each segment, and a 

 longer set which pass through several segments ; they are contained 

 in fibrous sheaths of sarcolemma, having large nuclei projecting 



