. The microscope and its revelations. er are the comparatively large (as much asI mm. in diameter) single-celled forms which are remarkable for theconstant presence of large dark brown granules, which an- scatteredirregularly round the central capsule and cover the greater part ofits outer surface. The nucleus is large, the capsular membrane isalways double, and is pierced by one or more large openings ; thewhole cell is inclosed in a thick gelatinous covering, and there isnearly always a well-developed extracapsular silicious skeleton,according to the structure of which the group is subdivide
. The microscope and its revelations. er are the comparatively large (as much asI mm. in diameter) single-celled forms which are remarkable for theconstant presence of large dark brown granules, which an- scatteredirregularly round the central capsule and cover the greater part ofits outer surface. The nucleus is large, the capsular membrane isalways double, and is pierced by one or more large openings ; thewhole cell is inclosed in a thick gelatinous covering, and there isnearly always a well-developed extracapsular silicious skeleton,according to the structure of which the group is Collozoa.—To this group belong those remarkable compositeforms which, exhibiting the characteristic radiolariaii type in their 1 The general plan of structure of the Ioliji-ijuthiii, and the signification of theirimmense variety of forms, were alily discussed \>\ Mr. \Valhcli in the. Trans, of iheiiTiiKr. Sue. vol. xiii. lH(), p. On reproduction in this group, cf. A. Borgert, Ziiol. Anzrig. xix. (IMOfi), p. RADIOLAEIA 853 individual zooids, arc aggregated into masses in which the skeletonis represented only by scattered spicules, as in Sphcerozoum (fig. (352)and Tlialassicolla, Tliese sea-jellies. which so abound in the seas ofwarm latitudes as to be among the commonest objects collected bythe tow-net, are small gelatinous rounded bodies, of very variablesize and shape, but usually either globular or discoidal. Externallythey are invested by a layer of condensed sarcode. which sends forthpseudopodial extensions that commonly stand out like rays, butsometimes inosculate with each other so as to form a network. To-wards the inner surface of this coat arc scattered a great number ofoval bodies resembling cells having a tolerably distinct membraiiiformwall and a conspicuous round central nucleus. Each of these bodiesappears to be without any direct connection with the rest, but itserves as a centre round which a number of minute yellowish-greenvesicles a
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicrosc, bookyear1901
