ZOOLOGY AND BOTANY, MICllOSCOPY, ETC. 585 



a stimulus inducing kinetic and directive responses, both through 

 changes of intensity and constant intensity. Unilateral elimination of 

 any part of the photoreceptive mechanism caused an unbalancing of 

 subsequent reactions. 



Striped Muscle of Limulus.* — H. E. Jordan has made a further 

 study of the skeletal muscle of Limulus (1) to test his previous 

 conclusions drawn from studies on the intercalated disks of vertebrate 

 cardiac muscle, that these disks are to be interpreted as " irreversible 

 contraction bands " ; and (2) to find additional evidence to refute the 

 theory that striped muscle can be interpreted in terms of " muscle-cells " 

 and intercellular myofibrillse. Both the skeletal and the cardiac 

 muscles of Limulus consist of trabeculse of finely granular sarcoplasm, 

 holding regularly aggregated collections of myotibrilla3, and confined by 

 a cell-membrane or sarcolemma; throughout the trabeculse are scattered 

 irregularly the numerous nuclei. In cardiac muscle the main trabeculse 

 and their branches form a loose-meshed syncytium. Neither type of 

 muscle contains mesophragmata. Very rarely an intercalated disk of 

 the simple-comb type appears in the cardiac muscle. Both types are 

 very similar in respect of the presence and arrangement, in the same 

 phase of contraction, of the disks and the telophragmata. These last 

 are continuous membranes closely attached centrally to the nuclear wall, 

 which is frequently drawn out into projections at the points of 

 attachment, and peripherally to the sarcolemma. The sarcolemma is a 

 very delicate membrane closely associated with the endomysium, but 

 reacting differently to specific connective-tissue stains. 



The evidence is unequivocal against an interpretation of structure in 

 terms of muscle-cells and intercellular myofibrillar. The nuclei of 

 the growing muscles multiply by amitotic division. The myofibrillar 

 may be resolved into still finer fibrils to the limits of visibility 

 (Heidenhain's "protomere" theory). The structurally different con- 

 stituents of the Limulus sarcostyle are the telophragmata (" ground " or 

 "Z" membrane) and the two disks ("Q" and "J"). These last, 

 which alternate, probably differ only in the presence of a greater 

 number of darker-staining " anisotropic " granules in the " Q " disk. 

 In essential structure the cardiac and skeletal muscles of Limulus are 

 closely similar, indicating a close functional similarity. The structure 

 is, moreover, a fine illustration of the " law of biogenesis," in that it is 

 practically identical with a stage in the early histogenesis of striped 

 muscle in teleosts. 



e. Crustacea. 



Photophores of Sergestes prehensilis.f — Arato Terao has made a 

 •careful study of the light-producing organs of this Decapod. With the 

 naked eye they are seen as minute reddish spots, 157 in number, widely 

 and definitely distributed. They give out dim greenish-yellow light in 

 an intermittent way, each time starting suddenly and vanishing with as 



* Carnegie Inst. Washington, Publ. No. 251 (1917) pp. 273-90 (3 pis.). 

 + Annot. Zool. Japon. ix. (1917) pp. 299-316 (3 figs.). 



Bee. 19th, 1917 2 R 



