322 JULIAN Ss. HUXLEY 
1 
the dense mass of yellow-brown cells are seen. (Zeiss ,',’’ water-immersion + 
4 compens. 0c.) 
Fig. 6.—Another spherule from the same specimen, same date. The 
layer of jelly is thinner. The spherule has subdivided into irregular masses 
with clear outer layer and yellow inner centre. From one, cells are beginning 
to separate. (Same magnification as 5.) 
Fig. 7.—Olynthus stages from restitution-masses, Osculum and oscular 
crown are well developed. (3+20c.) a. Large, fixed, of normal shape 
(spicules figured at the edge only). 6. Smaller, of abnormal shape (spicules 
omitted). A small patch (undotted in the figure) lacks the gastral layer. 
PLATE 14. 
Fig. 8.—A further stage in the development of the type shown in fig. 13. 
The gastral layer is markedly incomplete (spicules only figured at the 
edge). (3+4 0c.) 
Fig. 9.—Successive stage in one hanging-drop culture. (344 oc.) 
a. The chief masses present in the drop, two hours after isolation (four 
days from beginning of experiment). 6. After two days. The masses 
shown in (a) have fused together (in addition, in (a) there were three embryos 
and two small masses which had not fused). Note three larvae and one 
sphere partially attached. c. After four days. Larvae no longer visible, 
blow-out larger; more unification of the separate masses. d. After six 
days. No collars. Flagella shorter and fewer. Still more unification. 
Gaps in the blown-out region bridged by dermal membranes with amcebo- 
cytes on the inner surface. e. After nine days. Disappearance of blow- 
out. No collars or flagella. f. After thirteen days. Still further contrac- 
tion. A few cells had separated from the mass (not shown). 
Fig. 10.—To show the effects of mechanical shock. (3+4 0c.) a. A mass 
with good choanocyte blow-out and attached larva. b. The same mass 
after repeated pipetting. The larva is detached, the epithelium of the 
blow-out has contracted and thickened, the collars have been retracted. 
Fig. 11.—Restitution-mass with dermal epithelium and central dark 
yellow-brown sphere, separated from intermediate layers of collar-cells. 
(6+ 2 oc.) 
Fig. 12.—Small dermal blow-out under high power. (6+20c.) The 
dermal cells are granular. Adhering to the inner side of each are a number 
of finger-cells. A few dermal cells are figured in surface view. From others, 
the subjacent finger-cells have been omitted. Over the rest of the 
surface, dermal cells are not figured. The bulk of the interior mass 
is composed of choanocytes. From the edge of this, finger-cells protrude 
into the blow-out cavity. 
Fig. 13.—Very large dermal blow-out, spherical type. (3+ 4 0c.) 
Here there is no sharp internal mass, but the collar-cells form irregular 
areas of varying thickness adherent to the dermal epithelium. Those 
on the upper side are represented darker than those below. (The cells of 
the dermal epithelium have been represented too large.) 
