IO2 



HISTOLOGY 



LITERATURE 



SCHAFFER, J. "Zur Kentniss der glatten Muskelzellen insbesondere ihrer Verbindung," 



Zeits. f. Wiss. Zool., Band LXVI. 

 ARNOLD, J. " Uber Structur und Architectur der Zellen. 3, Muskelgewebe," in Arch. f. 



mik. Anat., Band LII. 



UNUSUAL FORMS OF MUSCLE 



Muscle, as has been said, must be developed wherever needed. Hav- 

 ing accounted for some of the usual places and methods of formation, 



we find a few very unusual 

 forms which cannot be brought 

 under the other classifications. 

 An example of such a pe- 

 culiar muscle cell is to be seen 

 in the large epithelial cell that 

 lies next to the water pore in a 

 sponge, Leucosolenia(Fig. 101). 

 The edge of this cell is trans- 

 formed into a fiber-bundle that 

 surrounds the pore, and, by 

 contracting or relaxing, it reg- 

 ulates the flow of water. The 



FIG. 10 1. Part of the body wall of a simple 

 sponge, Leucosolenia. f.vac., food vacuoles in en- 

 dodermal cells ; mus.c., muscle cells surrounding 

 the water pore (p.) ; spc., spicule. X 900. 



outline of this cell is not to be 

 seen, but is undoubtedly a defi- 

 nite outline and perhaps a 

 It could be brought out, per- 



regular one, like most epithelial cells, 

 haps, by the use of silver nitrate 



Another muscle is peculiar from the remarkable way in which its 

 cell-body is separated from the myo-fibrils. This is seen in the muscle 

 of the parasitic Cercaria from Helix. The cell-body of this muscle 

 cell lies entirely apart from the fibrils and sends to each one a single 

 strand of cytoplasm to support it (Fig. 102). It is probable that each 

 strand covers all of the fibrils that it goes to, on account of the needs of 

 trophic and functional support. A fibril cannot act alone if any of our 

 conceptions of muscle activity be near the truth. The fibril must have 

 some portion of sarcoplasm in contact with it to furnish it (according to 

 Englemann's theory) with the requisite heat-oxydization that causes it 

 to swell and shorten. 



The stalks of some Protozoa, as Vorticella, are capable of a very strong 

 and rapid contraction (Fig. 103). This seems ,again to be a case where 

 protoplasm cannot contract with sufficient efficiency, but yet is capable 

 of developing an arrangement which can so contract for it. The fibril 



