SEA-FISHERIES LABORATORY 861 
maximus can resist a considerable pull for a short time, 
4,000 grams are not sufficient to pull the valves apart 
unless acting for some time, when, as is the case with 
other lamellibranchs, a much less weight suffices to open 
them, in fact, as has been shown, starfishes are able to 
open oysters by a sustained pull. Corresponding to these 
differences in appearance and function there are 
differences in the histology of the two regions. The fibres 
of the large, rapidly contracting part, when seen in 
sections, show a very obvious striation, the smaller portion 
of the muscle consists of smcoth fibres. This relation 
between the cross striation of muscle fibres and rapidity of 
movement is of general occurrence (13 & 15). The 
striated fibres are very much flattened so that they can be 
seen either in surface or in edge view (fig. 30, 6. and a.). 
If small portions are fixed in osmic or Flemming and 
stained with iron haematoxylin it is quite obvious that the 
striping consists of distinct transverse bands; there is no 
possibility of its being only an appearance due to fibrillae 
being thrown into spirals when in a contracted state. 
The dark bands are three or four times as long as the 
light, almost unstained, portions. Moreover, the fibres 
have a series of constrictions which correspond in position 
with the hight stripe; this can be seen extremely well if 
a fibre is observed in edge view, so that the dark portions 
correspond to the swellings and the light stripes to 
constrictions. 
The difference in intensity of the stain taken up by 
the two parts, however, is so great that it would be 
difficult to affirm that the dark stripes are due to a greater 
thickness of stained protoplasm, though it is possible that 
this may be the case (see 14). 
The nuclei of the fibres are not frequent in occurrence, 
and are pushed rather to one side of the fibre and elongated. 
