466 EIOHARD EVANS. 



15 fi across, while the osculum measures from 60 to 70 /*. Compare the 

 figures on Plate 39. 



PLATE 36. 



Fig. 9. — x 350. Entire section of a larva, type B. Note the flagellated 

 layer (/, c.) covering the whole surface ; inside the flagellated layer the cells 

 with granular nuclei (c. y. n.) forming a lining to the larval cavity as well as 

 scattered about in the solid part of the inner mass ; the cell groups (ff. c.) 

 deeply embedded, as a rule, in the inner mass ; and finally the cells with 

 vesicular nuclei {c. v. u.), containing numerous yolk bodies and usually only a 

 single nutritive vacuole (n. v.), coloured black in one half but clear in the 

 other half of the figure. The section from which this figure was drawn was 

 bleached with chlorine, which rendered the nutritive vacuoles clear, as repre- 

 sented in the right half of the figure ; in the other half they are represented as 

 seen in the section before bleaching. 



Figs. 9 a and 9 b. — x 1000. Figures drawn from the same larva as Fig. 9, 

 introduced to show the groups of small cells (^. e.) with their small nuclei 

 {n. ff. c), which are seen in the centre of Fig. 9 « as a patch, but in Fig. 9 b 

 as a ring round the periphery of the undivided cytoplasm. In these two 

 figures the same group of small nuclei is represented in successive sections. 



In Fig. 9a the group has been cut tangentially, and both tlie common 

 membrane by which they are surrounded and the faint lines which separate 

 them can be seen. These faint lines represent the first appearance of the cell 

 walls in the multinucleated cytoplasmic mass. 



In Fig. 9^ the group has been cut radially ; the nuclei, therefore, appear in 

 the form of a ring round the cytoplasmic mass in which they lie. There are 

 faint dividing lines to be seen passing between the nuclei which stretch across 

 the central space. 



Fig. 10. — X 1000. Tangential section of a larva of type D, the fourth 

 section of the series. The nuclei of the flagellated cells {n.fl. c.) are cut 

 transversely, and are therefore circular in section. The cells with granular 

 nuclei occupying the centre of the section are branching and irregularly 

 shaped cells, and are far from forming a complete membrane even at this 

 stage. The nuclei of the flagellated cells in some places appear to lie within 

 the cells with granular nuclei, but a radial section proves that this is a de- 

 lusion ; they merely lie close to one another. 



Fig. 11. — X 350. Entire section of a larva of type C. The flagellated 

 cells are much the same as they were in Fig. 9. The cells with granular nuclei 

 (c. g. n.) are smaller, and are extremely flattened towards the larval cavity. 

 The cell groups are in many cases completely divided and form chamber-like 

 rings, the individual cells of which are often provided with a collar and a 



