Structure of Liniulus Heart Muscle. 409 



cylinder with its limiting membrane and peripheral nuclei bears to 

 the contractile portions within. The boundary line at first sight is 

 strikingly similar to the membrane Ileidenhain figures as a sarco- 

 lemma (1901) in human heart muscle. There is the same proto- 

 plasmic area just outside the outermost fibril and the membrane 

 arches in festoons to meet the Z line. This gives the same effect that 

 McCallum describes in mammals (1897), where he says the rounded 

 edge of the sarcoplasmic discs makes up the edge of the fiber. The 

 presence of nuclei just beneath this membrane seems opposed to the 

 view that a sarcolemma is present unless it is assumed that there 

 are two kinds of nuclei present in the fiber, one being at the periphery 

 to attend to the growth of the cell. The facts are without question, 

 it being merely a matter of interpretation. Of course if the trabec- 

 ulse were considered as having a sarcolemma the strands within could 

 no longer be considered as the real heart fibers. The structure would 

 still be a syncytium, but the significance of the secondary syncytium 

 within the trabeculse would be changed. 



Most observers, however, agree that the lower forms do not have 

 a sarcolemma (Renaut et Mollard, 190-1), the heart fibers being bare. 

 The simpler explanation would be that the trabeculae are provided 

 with a connective tissue sheath. This Avas tested by using standard 

 connective tissue stains, and it was found that the limiting mem- 

 brane stained blue with Mallory's and pink with Van Gieson's. 

 Van Gieson's was not entirely decisive, however, since the Z line 

 also took the same color. By keeping sections twenty minutes in the 

 acid fuschin solution of Mallory's stain and then reducing the time 

 in the aniline blue solution to about three minutes, it was found that 

 the limiting membrane always stained blue, while Krause's mem- 

 brane often took a bright purple color. This differentiation in color 

 would indicate that the two structures were different. Heidenhain 

 (1901) found that vanadium hsematoxylin stained the sarcolemma and 

 the Z line both blue, connective tissue taking a much lighter bluish 

 color. In Limulus sections vanadium haematoxylin stained the base- 

 ment membrane a faint blue and the muscle substance an orange, 

 which seemed to indicate that the stain was ripe and working prop- 

 erly. The membrane in question, however, seemed little if at all 



