314 Relation of Xervous System to the Developing Musculature 





4 



leg 



II 



reared in 0.02 per cent solution, had in five minutes recovered sutiiciently 

 to swim several strokes, and in seventeen minutes the co-ordinated move- 

 ments of this specimen could not be distinguished from those of a per- 

 fectly normal larva. In other cases the recovery of palustris larva? was 

 found to be considerably more rapid than in the experi- 

 ment just described in full though it was never so rapid 

 as is the case with virescens larvae. It is clear then that 

 the mechanism requisite for carrying out the complex 

 ^ ^ muscular movements of locomotion and respiration de- 



\'-W ' velops nornuilly without ever having functioned, although 



in the normal development of the embryo, the acquire- 

 ment of this power is a gradual one, being accompanied 

 > ^ l)y the frequent activity of the parts. 



The irritability of the developing embryos was tested 

 in the experiments from day to day by stimulation with 

 a needle-point. 'No reflex response was ever observed at 

 any stage in embryos reared in solutions of 0.03 per cent, 

 except in a few doubtful instances. Nevertheless it 

 seemed safer to experiment with somewhat stronger solu- 

 tions (0.035 to 0.03 per cent), in which no embryos ever 

 manifested any reflex activity -whatever. Electrical 

 stimuli were not tried, but it was observed that the 

 drugged organisms were not sensitive to chemical stiinuli, 

 for in putting them into the ordinary fixing fluids, such 

 as mercuric chloride or formalin, no movements were 

 ever observed, while nornuil embryos contract their 

 muscles violently. The irrital)ility of the muscle itself 

 remains, however, even in embryos kept in the stronger 

 solutions of tlie drug, but the eifect of direct stimula- 

 tion of the muscles may readily be distinguished from 

 that of the indirect or reflex irritation. The former 

 is evidenced by a sharp tonic contraction of the myo- 

 tomes on the same side of the body and immedi- 

 ately at the point of application of the needle prick; 

 moreover, this type of contraction takes ]3lace only on 

 strong stimulation, often only when the muscle is actually pierced by 

 the point of the needle. The reflex response of normal embryos is quite 

 different from this. If one stimulates a young embryo by lightly touch- 

 ing it on one side of the body, the first response is a general contraction 

 of the myotomes usually on the opposite side of the body, followed by the 

 alternate contraction of the two sides, Avhich results in a co-ordinated 





I'M'' 



Fig. 18. Mus- 

 cle fibers fi-om 

 myotome at base 

 of tail of larva 

 kept six days in 

 acetone - chloro- 

 form. 



