On the Minute Structure of Striped Muscle, SfC. 301 



occur the fibres are encircled by a thicker band of int9r6brillar sub- 

 stance, that the little beads or swellings in the diagrams are merely 

 optical sections of the thicker parts of the honeycomb. These 

 thickened portions, when very strongly differentiated from the fibrils, 

 as by the gold method, may appear like transverse bars running 

 across the fibrils in the region of the clear stripe, and the whole 

 structure has unfortunately been misinterpreted by some observe! s 

 into a network, the transverse links of which are the encircling and 

 thickened parts of the honeycomb, while the longitudinal threads are 

 the lines really marking the optical section of the honeycomb tubes. 

 If any threads of tissue are to be actually seen, I quite agree with 

 Professor Klein in ascribing them to precipitation within the inter- 

 arillar honeycomb. 



The Physiological Explanation of the Varicosity. 



I may not unreasonably be asked to supply some hypothesis of my 

 n in place of the exploded theories of imbibition, for, if we simply 

 iew a muscle fibre as consisting of varicose fibrils, we have a bare 

 lorphological fact without any physiological significance. Before 

 oing this, I will venture to clear up one misunderstanding which has 

 arisen concerning the morphological difference between striped and 

 triped muscular tissue, although this question will, I hope, be 

 ire fully discussed in a subsequent paper. 



The unstriated muscle is generally described as a nucleated spindle, 

 presenting fine longitudinal fibrillation, and devoid of a true sar- 

 colemrna, while the striped or voluntary fibre is described as a 



;rillated thread of contractile tissue, invested by a sarcolemma 

 derneath which numerous nuclei are placed. The heart muscle is 

 generally looked upon as a tissue intermediate between the two. 

 ut authors to whom we owe these ideas, have restricted their 

 quiries to the Vertebrate histology alone. It is necessary to pass 

 the region of comparative histology, before we can thoroughly 

 >mprehend the subject. If we do this, we shall find that there are 

 o chief varieties of fully differentiated muscular tissue. First of 

 , there is the nucleated spindle devoid of sarcolemma and made tip 

 fibrils cemented together, and we notice that these spindles may be 

 iped or unstriped, the difference depending upon the rapidity of their 

 traction. They are found in most divisions of the animal kingdom ; 

 us, in the adductor muscles of Cardium, Pecten, Lima, rapidly 

 iving Lamellibranchs, we have nucleated and striped spindles ; 

 ese occur in the heart muscle of the Frog and many other animals, 

 hile non-striped spindles are found in parts of the circulating and 

 igestive systems where less active movements are required. 

 Then again, there is another type of muscular tissue, consisting of 



