. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. Section of macrospore of Pilularia some time after germination, 50 diam. a, two layers of the exospore, the outer, vertically striated, the inner, homogeneous; b, cavity of endospore bounded superiorly by the prothallium, the papilkcform summit of which projects through the canal of the exospore. which is surrounded by a white coriaceous exospore. This last exhibits two distinct layers, of which the internal is colourless and vitreous, without trace of structure ; while the external appears to be formed of prismatic colu
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. Section of macrospore of Pilularia some time after germination, 50 diam. a, two layers of the exospore, the outer, vertically striated, the inner, homogeneous; b, cavity of endospore bounded superiorly by the prothallium, the papilkcform summit of which projects through the canal of the exospore. which is surrounded by a white coriaceous exospore. This last exhibits two distinct layers, of which the internal is colourless and vitreous, without trace of structure ; while the external appears to be formed of prismatic columns fitting closely together, which are more distinct at the lower end of the spore, while they disappear entirely towards its smaller end or apex, at which point the exo- spore forms a papilliform projection open at its summit. From this arrangement there results a canal, which is immediately sur- rounded by the thickened and dentate margin of the vitreous layer, and leads to the apex of the endospore. 2-to 98. The prothallium.—The first indication of the commencement of the germination of the macrospore is the formation of a lenticular accumulation of granular plasma, at the sum- mit of the endospore, which had previously contained only starchy, mucous, or oleaginous granules. Soon after there appears in the same position a delicate cell of similar form, the upper surface of which is in contact with the endosporal membrane, and is immediately subjacent to the aperture in the exospore. It is in all probability from this cell, although the earlier stages of the development have not been clearly made out, that the prothallium takes its origin. A day or two after germina- tion it consists of a central cell, which is sur- rounded by a single layer of others of smaller dimensions. Four of these last are invariably found interposed between the upper surface of the large cell and the spore membrane ; the septa by which they are separated being per- pendicular, and at right angles
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