286 Papers from the Department of Marine Biology. 



that produced by the telophragmata in certain distorted fibers, as shown 

 in figure 4, which also is not the case. 



In this connection should be considered the careful work of Meigs (16) 

 (1908) on the wing-muscle of the fly. He recognizes the existence of 

 at most only 3 different substances in the sarcostyle, that of the Q 

 bands and that of the Z and M lines. He regards J as the optical effect 

 of reflection phenomena due to the presence of Z. He conceives of 

 Z as a substance more highly refractive than its surrounding medium 

 Q. His identification of M as a true membrane in the wing-muscle 

 of the fly is at variance with the observations on the wing-muscle of 

 beetles by Thulin (4) who records its absence in this group. In Limulus 

 striped muscle, both cardiac and skeletal, M-membranes can not be 

 discerned either in fresh or fixed and stained material. 



In unstained skeletal fibers the Q-band is faintly visible; in cardiac 

 muscle it can only occasionally be barely detected. But in stained 

 fibers in certain instances it is distinctly visible in both types of muscle 

 (figs. GB and 9). Certainly Q and J have a different staining capacity; 

 and this indicates a structural difference, perhaps inhering only in a 

 relatively greater abundance of "anisotropic granules" in Q. 



The J-band, compared with the Z-membrane, is much too wide to 

 permit of any reasonable interpretation of its appearance in terms of 

 refraction phenomena due to the presence of the Z-membrane. More- 

 over, in the contracted fiber one sees only " contraction bands" (appar- 

 ently Z + Q), and J-bands, the J-band being now topographically in 

 part at the former level of the original Q-band. In the case of Limulus 

 striped muscle, one is forced to conclude that 3 distinct substances are 

 present, namely, that of the telophragmata and the J and Q substances. 



Limulus increases in size at least throughout early life. Histologi- 

 cally the tissues of the internal organs mature early, but provision 

 must be made for constant enlargement. This fact must be kept in 

 mind in the interpretation of the structure of its muscle. Though 

 mature as concerns its fundamental histogenesis, it presents develop- 

 mental phenomena. It is of cardinal interest and significance that these 

 are very similar to early histogenetic stages in the muscle of higher 

 forms. In skeletal muscle this point concerns chiefly the arrange- 

 ment of the fibrillse in lamellse and cylinders, each undergoing longi- 

 tudinal splitting, the former both radial and vertical (paratangential) . 

 This is exactly the condition prevalent in developing muscles of the 

 newly-hatched rainbow trout and other teleosts. In cardiac muscle 

 this same point concerns also the nucleus. These nuclei multiply 

 greatly, and by amitotic division. The reason for amitotic multipli- 

 cation rather than mitotic in the enlarging Limulus muscle, both 

 skeletal and cardiac, remains obscure. 



This leads naturally again to a consideration of the evidence for 

 "muscle cells" in the sense of Apathy (1888) and Baldwin (1912). 



