78 THE AMERICAN MONTHLY [Manh 



iiieasuiini; only an average of ]() niicron.s at the 2()-(iay 

 stage. 'I'liis would be expected from the physiological 

 conditiiius of inactivity. 



Fai'Ts from AnuLT Fokms.^As the skeletal muscle is 

 looked upon as the most liighly develo})ed, consequently 

 an examination of striped muscle which is not voluntary 

 may also throw some li*;lit ujion the .subject under con- 

 sitleration. Of these forms, tlio cardiac is most sugges- 

 tive; the tibre in it is much shorter and contains only 

 one centrally placed nucleus. This tlien is less special- 

 ized than the striped muscle fibre of the frog for one 

 centrally ])laced nucleus is a characteristic of the 

 [)lain muscle fibre. The question arises, is there any 

 striped muscle, otherwise placed, which may show some 

 ditferencey The muscle in the esophagus offers a basis 

 for comparison. Sections both longitudinal and trans- 

 verse have been examined from the various parts of the 

 tubes of some of the animals already noted. The esopha- 

 gus of the frog has only plain muscle. The ral)bit's 

 esophagus has plain muscle fibre at the stomach end, but 

 this gradually changes toward the other end where the 

 striped muscle fibre is like the skeletal muscle in the 

 ])Osition of its nuclei. The average ]>er cent of nuclei 

 imbedded in the sarcous substance is l-j per cent, but 

 the variation from the middle of tube to the mouth end 

 is from 4 per cent to per cent. Nothing like cardiac 

 muscle, in the gradual change, could be observed, though 

 some writers state that fibres become short toward the 

 uii<ldle ot' the es(ij)hagus. The cat's esophagus has also 

 plain muscle at the stomach end and gi-adually changes 

 to striped muscle toward the other end. It has an 

 average of 20 ])ei- cent of nuclei iinbed(le(l in the sarcous 

 substance. This large number may be due to the fact 

 that the sections, from which the observations were 

 made, were of tissue ([uite far down this tube. Taking- 

 it. ht»wever. as correct on the wlntle. tlie position of the 



