474 RICHARD EVANS. 



PLATE 41. 



Figs. 32 a — d. — x 1000. Four successive sections of tlie same flagellated 

 chamber, drawn to show the nature of the iuhalant canal and pore. The canal 

 which is drawn is an exceedingly short one, and passes straight from the sub- 

 dermal cavity above into the flagellated chamber below. 



a shows how the layer of flat epithelium {jl. ep.) forms a depression round the 

 entrance of tiie canal, the cell below forming, apparently, the actual wail of 

 the canal itself. 



b shows tlie canal {i.p.) along its wiiole length, save a small portion near 

 the surface, where it is covered over by the flat epithelium which lines the 

 subdermal cavity {S. C. in a). On one side a flattened cell is seen to line the 

 canal, but there is no nucleus anywhere. 



c shows the same canal or pore {i. p.) opening into the flagellated 

 chamber. It appears to be surrounded by the same cell on all sides, and the 

 cell in question is distinct from the flat epithelium of the subdermal cavity. 



d shows no sign of the canal, but a large cell with a vesicular nucleus 

 occupies the position taken up by the canal in figs, b and c. The cell in 

 question {c.v. n.) is the same cell as lines the canal in the other figures, and is 

 perforated by it. 



Fig. 33. — A flagellated chamber with a short inhalant canal and inhalant 

 pore (i.p.). Apparently both the canal and pore are lined by the same cell, the 

 nucleus of which is not seen. 



Fig. 34. — x 1000. The same inhalant canal (/. C.) and pore (i.p.) in the 

 section succeeding the one drawn in Fig. 33. In this section the nucleus of 

 the pore cell is seen, and is evidently a vesicular nucleus in the process of 

 transformation to the granular condition. 



Fig. 35. — This figure represents a section of a flagellated chamber, and 

 shows two things: 



(1) A collar-cell which has withdrawn its collar and flagellum, and contains 

 a nucleus in the spindle form, showing clearly that the cells of the flagellated 

 chambers divide by karyokinesis. Note that the longitudinal axis of the 

 spindle lies in a plane tangential to the wall of the flagellated chamber. The 

 cell must therefore divide longitudinally. 



(2) A transverse section of a spicule {sp.) lying in the scleroblast, a cell 

 with a vesicular nucleus (v. n.) against which the spicule presses giving it 

 a crescentic appearance. 



Figs. 36 a — d. — x 1000. Four stages of growth of the megascleres. 

 The spicule in each case is completely enclosed by the scleroblast. In 

 Fig. 36 « the nucleus is vesicular as well as in 36^; but in Fig. 36 c it 

 begins to lose its vesicular character, and tends to become granular. In 



