. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . likefissures, one on the inner side and one on the outer side of each valve. The raphe is interrupted by the central nodule which is perforatedby two canals, each of which joins together the outer and inner fissures ofone half of the valve. There is also a canal running along the inner side of The 93 the central nodule joining together both halves of the inner fissure (fig. 652 schl). The inner fissure terminates at each end of the valve in a
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . likefissures, one on the inner side and one on the outer side of each valve. The raphe is interrupted by the central nodule which is perforatedby two canals, each of which joins together the outer and inner fissures ofone half of the valve. There is also a canal running along the inner side of The 93 the central nodule joining together both halves of the inner fissure (fig. 652 schl). The inner fissure terminates at each end of the valve in a funnel-shapedstructure which projects into the cavity of the terminal nodule (fig. 65 3tk).The outer fissure terminates in a definite polar cleft, which is a curved slitin the terminal nodule (fig. 65 3 psp). The polar clefts (often called terminalfissures) at the extremities of the same valve are usually curved in the samedirection, but a number of species are known in which they are curved inopposite directions. The corresponding clefts of the epivalve and hypovalveof a single individual are invariably curved in opposite directions (fig. 65 4)-. Fig. 66. Surirella Capronii\~Br&o. var. calcarata (Pfitzer) Hustedt. 1, transverse section acrossthe cell showing the four wing-like expansions (fl), each with its raphe-canal (r). 2, trans-verse section of wing, showing raphe-canal and outer cleft. 3, longitudinal section of , wing viewed from the edge, qk, cross-canals; zw, thin intercalary pieces of wing; Ik, raphe-canal (or plasma-canal); sp, cleft of raphe. From Oltmanus (after Lauterborn). The somewhat complex system of clefts and canals described aboveis concerned with streaming movements of the cytoplasm, the latter beingbrought into direct contact with the surrounding medium by means ofthe outer fissure of the raphe. This is stated by 0. Miiller to be the directcause of the curious movements of those diatoms which possess a true raphe.(Consult page 102.) The raph
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