126 Marvels of Pond-Life. 



reduced to its simplest and essential form. A muscle 

 may here be viewed as a beautiful dissection far sur- 

 passing the most refined preparation of the dissecting 

 needle^ for it is composed of a bundle of elementary 

 fibres, totally separate from one another through their 

 entire course." He further adds, " The fibres of the 

 great retractor muscle are distinctly marked by trans- 

 verse striae ; — a condition, however, which is not at all 

 times equally perceptible, and some of our best ob- 

 servers have denied to the Polyzoon the existence of 

 striated fibre. '^ 



We can confirm the fact of this sort of fibre being 

 present, but we fancy a reader not versed in the 

 mysteries of physiology exclaiming, ' What does it 

 matter whether his fibres are striped or not ?' 



Physiologists used to suppose there was a strong and 

 marked distinction and separation between striped 

 muscles, that is, muscles the fibres of which exhibit 

 transverse stripes when magnified, and those which do 

 not. KoUiker, however, says this decided separation 

 can no longer be maintained,"^ and he gives instances 

 in proof of the connections that can be traced between 

 the two forms. In the higher animals the striped 

 muscles are the special instruments oiwill, and of move- 

 ments that follow, or are accompanied by, distinct sensa- 

 tions. Striped fibre must be regarded as the highest 

 form ; and as a muscle of this sort contracts in length 

 it increases uniformly in breadth. 



There are many other genera and species of fresh- 

 water polyzoa besides the Plumatella repenSj and they 

 * ' Manual of Human Microscopic Anatomy/ p. 63. 



