322 E. A. MINCHIN. 
Clathrina contorta and C. lacunosa. I believe, how- 
ever, that in an earlier stage the secondary monaxons would 
be found to be covered by six cells, of which two wander off, 
leaving the two remaining pairs to secrete the spicule. On 
this view the secondary monaxons would be comparable to a 
certain extent with the derelict spicules described above. I 
regret that I am not able to bring forward concrete evidence 
for these conclusions. 
VI. Histrotocgica, Notes; THE Excretory CELLS OF 
LEUCOSOLENIA COMPLICATA. 
The dermal epithelium of Leucosolenia may vary greatly 
in form, as Urban (1905, p. 53, pl. vi, figs. 42—62) has 
pointed out for another species. Some cells are of the 
conventional flat type (figs. 43, 54—57), from which every 
gradation can be found to others which have the nucleus 
placed deeper and are more flask-shaped (figs. 388,47). Near 
the point of attachment the epithelium becomes of a pro- 
nounced columnar type (fig. 45). The species of Leuco- 
solenia are very slightly, if at all, contractile, and contrast 
sharply in this respect with the Clathrinide. Hence, in 
agreement with Urban, I do not think that the flask-form 
can be explained in this genus as the result of contractility. 
T am not inclined, however, to regard the dermal epithelium 
as generally glandular, though it is very probably so in the 
region of the point of attachment. The clear protoplasm, 
free from coarse granules, of the general dermal epithelium 
does not suggest secretory cells. I regard the polymorphic 
nature of the dermal epithelium as due to the fact that it is 
practically a layer of amoeboid cells, which are continually 
immigrating into the interior to form spicules and returning to 
the surface again. The power of concerted contractility 
possessed by the dermal epithelium of Clathrinide has 
apparently not been acquired by the Leucosoleniide, 
which in many respects present more primitive characters. 
In the collar-cells, for instance, the nucleus is terminal, as in 
