Uavesport. — Buddins in Brjozoa. 



PLATE XL 



ABBREVIATIONS. 



cev. ooe. Neck of ooecium. ms'drm. Mesoderm. 



ccel. Coelom. oui. Ocecium. 



ec'drm. Ectoderm» ou.' Oublasis. 



en'drm. Entoderm. pyd. Polypide. 



ex. Outer layer of bud. sto. Stolon. 



i. Inner layer of bud. tct. Koof of stock. 



III. gm. Lumen of the bud. 



Fig. 93. A portion of a longitudinal section through a young stock of Plumatella 

 polymorpha, about two weeks after hatching from statoblast (killed 

 12th May, 1890), showing the body wall just analward of the neck of 

 a young polypide {pyd.), at the oral side of which a younger bud has 

 already arisen. The inner (mesodermal) layer of the body wall 

 shows ooblasts (ov.') in various stages of development. X 600. 



Fig. 94. Longitudinal section of ocecium of Cristatdla showing embr3'0 which is 

 giving rise to the coelomic epithelium by ingression of cells at its 

 proximal pole, — i. e. the pole nearest the neck of the ooecium. There 

 are in the next section two other cells in the cavity of the blastula, 

 one of which appears degenerate in that it contains a huge vacuole, 

 and has no distinct nucleus, the chromatic substance lying scattered 

 loose near the cell wall. X 600. 



Fig. 95. Longitudinal section through ooecium of Cristntelln and its contained em- 

 bryo. One polypide bud and the stolon [sto.) are shown here. There 

 are two other buds in the embryo further developed than this one, 

 lying to one side of it, and on the side of each of these buds is the 

 Anlage of another. The stolon is seen to be well developed, lying be- 

 tween tiie ectoderm and mesoderm throughout the region bounded 

 by the three older buds, and extending as a zone be3'ond them, and 

 even beyond the Anlage of the youngest polypides. The embryonic 

 tissue thus forms a disk about 75 X 150 ;u in extent. X 300. 



Fig. 96. Transverse section of ooecium of Plumatella, showing origin of first pol- 

 ypide. Compare with Figure 99, which represents an earlier stage. 

 X 390. 



Fig. 97. Longitudinal section through ooecium and contained embryo of Cristntelln. 

 The stolon is already cut off from tlie ectoderm. Tiiis stage imme- 

 diately follows that of Figure 101, Plate XII. The forming bud is 

 that of tlie first polypide. X 390. 



Fig. 98. Oblique section through ooecium of Plumatelln,?.how\ng: a later stage in 

 development of the inner layer of the larva (cf Fig. 94). X 600. 



Fig. 99. Longitudinal section of ooecium and contained larva of Plumatella. The 

 bud shown at /., ex. is the first in the colony. An incipient (second) 

 bud is shown five sections to one side in the region indicated by an 

 asterisk. X 410. 



