ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 941 



Striped Muscle of Arthropods.* — Herr A. v. Gehuchten has re- 

 investigated the much studied structure of the striated muscles of 

 Arthropods. He distinguishes the yellow muscles of the appendages 

 from the white muscles of the wings. 



(1) The muscles of the appendages. After describing the well- 

 known phenomena, the author notes the differences observed when the 

 reagent is coagulatory in its action and when it is dissolvent. In the 

 fibre there are two portions, one soluble in dissolvent reagent, the other 

 persistent. The latter has a structure and takes the form of a network 

 — it is the protoplasmic reticulum. The former is more or less fluid, 

 rich in albumen and especially in myosin, it is the " enchyleme myosique." 

 These two portions exist in the living fibre ; the transverse strife of the 

 clear zone and the longitudinal filaments of the darker band belong to 

 the reticulum ; the dull and homogeneous basis of the dark band is the 

 enchylema. With a coagulating reagent the reticulum is rendered stiff 

 and brittle ; in the enchylema the albuminoid substances are citagulated 

 around the longitudinal trabeculae of the reticulum. The phenomena of 

 discs, fibrils, &c., are explained in terms of these observations, and the 

 structural identity of muscle-cell with any ordinary cell maintained. 



(2) In the muscles of the wings, the structure is quite different. 

 There one finds the fibrils of Krause. Each fibril is inclosed in a 

 cylindrical tube divided into cases by complete transverse membranes. 

 The divisions are filled with enchylema. The fibrils are usually united 

 into bundles (without sarcolemma) by interfibrillar granular substance. 

 The striated muscles of Vertebrates agree in structure with what has 

 been described in regard to the muscles of Arthropod appendages. 

 Finally the complicated structure of the nuclei of the muscles in the 

 frog is described. 



a. Insecta. 



Primary Segmentation of the Germ-stripe of Insects, j — Prof. v. 

 Graber has been investigating the early stages of development in Insects. 

 He finds that the germ-band is at first either discoid (as in Stenohotlirus 

 and CEcanthus) or more elongated (as in Hydropliilus, Lina, &c.). The 

 discoid portion corresponds chiefly to the antennary segment, while the 

 primitive trunk has at first a comparatively slight extension. In a few 

 cases two transverse grooves arise simultaneously, thus giving rise to 

 three primitive segments, which appear to correspond to the three 

 primary divisions of the adult body (head, thorax, and abdomen). The 

 priniitive trunk of the germ-band of Stenobothrus and CEcanthus is not 

 segmented, as has been hitherto supposed for Insects, into the permanent 

 segments (metameres or microsomites), but three larger sections (macro- 

 somites) are formed. Of these three segments of the primitive trunk 

 the first correspond to the sum of jaw-bearing metameres, the second to 

 the sum of leg-bearing metameres, and the third to the abdomen. In 

 the primary or macrosomitic segments of the primitive trunk of Steno- 

 bothrus there is not merely an external jointing, but a complete division 

 of the hypoblast. 



The secondary or microsomitic segmentation of the primitive trunk 

 does not in Stenobothrus and Lina (any more than in Spiders — Morin) 



* Arch. Anat. u. Physiol. (Physiol. Abth.), 18S8, pp. 5G0-4. 

 t Morphol. Jahrb., xiv. (1888) pp. 345-68 (2 plti.)- 

 1888. 3 S 



