SOOLOGY AND BOTANY, MICROSCOPY, ETC. 393 



and Oxystomata ; no brachyurous crab occurs in the deepest abysses of the 

 ocean (beyond 2000 fathoms) and but very few at depths below 500 fathoms. 

 Some of the deeper water forms were found to have a wide geographical 

 range. Among the Pinnotheridge the new subfamily of Hexapodinae is 

 instituted for those curious forms in which the fifth ambulatory legs are 

 rudimentary or aborted. The Leucosiidse it is proposed to divide into the 

 niinae and the Leueosiinffi. 



Structure of Muscular Fibres of Hedriophtlialniata.* — M. E. Koehler 

 states that in the hedriophthalmatous Crustacea the myogenic cell is not 

 entirely occupied by the contractile substance, and that a more or less con- 

 siderable portion of the protoplasm inclosing the nuclei persists in the 

 adult animal ; the muscular bundles are remarkable in that the contractile 

 substance occupies the central part of the cell, and the protoplasm the 

 periphery. The muscular fibrils are grouped into small columns, which 

 are very distinct, but their number, size, and relative disposition vary con- 

 siderably. Among the Amphipoda, Gammarus pidex has the primitive 

 cylinders very distinct ; they are of some size, and to the number of ten to 

 fifteen occupy the central part of the cell ; in Talitrus salfator the cylinders 

 are smaller, but more numerous ; in Dexamine spinosa they are very small 

 and closely packed, and appear in section as fine granulations. Among the 

 Isopoda, Idotea linearis has numerous cylinders, rather closely packed, and 

 forming a central group which is surrounded by the richly nucleated proto- 

 plasm of the myogenic cell ; in SpJiseroma serratum the cylinders are very 

 large, the protoplasm very abundant, and the nuclei of considerable size. 

 In Ligia oceanica the myogenic cells fuse with one another, and the 

 primitive cylinders are grouped in such a way as to leave an interval 

 between themselves and the membrane of the cell ; this interval is occupied 

 by protoplasm, and the nuclei are small and not numerous. In Gonilera 

 cylindracea the primitive bundles are relatively colossal in size ; the 

 myogenic cells give rise to polygonal areas which may be as much as 

 0"08 mm. long and 0'025 mm. wide. In the parasitic Isopoda the 

 primitive bundles are also large. The number of primitive cylinders and 

 the size of the elements does not, in the Hedriophthalmata, appear to 

 increase in direct relation to the size of the animal, for they are common 

 in Gonilera, smaller in Cirolana, and still smaller in Ligia, while in Amphi- 

 pods they are larger than in Gammarus. The variations in histological 

 structure are seen to be less remarkable in Amphipods than in Isopods, 

 and in these latter orders there are often considerable differences in the 

 size of the muscle-cells possessed by one and the same animal. 



Development of Porcellio scaber.| — Dr. W. Reinhard comes to results 

 essentially different from those of Prof. Bobretzky and Herr Nusbaum as 

 to the formation of the germinal layers of Porcellio scaler; it may be 

 noted that he has had the opportunity of studying phases of development 

 earlier than those seen by the naturalists just mentioned. The nucleus of 

 the egg-cell divides, and forms amoeboid cells with part of the protoplasm ; 

 these, as they multiply, make their way to the periphery of the egg ; when 

 they reach it they become many-sided, and are converted into the cells of 

 the ectoblast; this is not at first a thick layer but consists of several 

 " islands." Under these several layers of cells appear, and between them 

 the spaces become gradually filled up ; the cells underlying the ectoblast 

 form the primary endoderm, which only gradually becomes differentiated 

 into mesoderm and endoderm. 



The midgut is formed as an independent portion from the endodermal 



* Comptes Eendus, civ. (1887) pp. 592-5. . f Zoal. Anzeig., x. (1887) pp. 9-13. 

 1887. 2 D 



