282 W. WOODLAND. 
Fic. 16.—Division of two of the trefoil cells—second stage in formation of 
sextet. 
Fic. 17.—The sextet stage. a@ presents the more typical appearance of 
this stage. 
Fic. 18.—The first appearance of the young triradiate spicule—the three 
granules or rods being quite separate. 
Fic. 19.—The junction of the three needles accomplished; thickening of 
the individual needles has also occurred. c and d show the hollow appearance 
due to corrosion by acid. 
Fies. 20—24 illustrate the further development of the triradiate spicule in 
S.coronata. Figs. 21 and 22 are quadriradiates, the gastral ray possessing 
one actinoblast. In both Figs. 23 and 24 two of the basal cells have slipped 
into one interspace—an unusual occurrence. 
PLATE 14. 
Figs. 25—30 continue to illustrate the further development of the tri- 
radiate spicule in S. coronata. Fig. 25 is a quadriradiate. 
Fries. 31—34.—Young stages of triradiate spicule formation in S. ciliata. 
The superior size of one of the three needles is manifest from the first. 
Figs. 35—40 show stages of gastral ray (quadriradiate) development, as 
seen in longitudinal and transverse sections of the sponge-wall. In Figs. 
35—38 the gastral ray possesses only one actinoblast. In Figs. 39 and 40 
the gastral actinoblast has divided. In Fig. 38 the cytoplasm has been slightly 
stained with Kernschwarz to exhibit its full extent. 
Fies. 41 and 42 show well the secondary thickening of the monaxon spicule 
due to the migration proximally of the distal scleroblast. In Fig. 41 is again 
well seen the pale ‘‘ mould” in the calcoplasm in line with the extremity of 
the spicule. 
Fras. 43 and 44 furnish evidence for the supposition that some monaxons 
arise from the association of two mother-cells. See also Fig. 3, a. 
PLATE 15. 
Fies. 45—49 are figures of longitudinal sections of the sponge-wall. Fig. 
45 shows the division of a scleroblast before it has immigrated from the 
gastral epithelium. Figs. 46, 48, and 49 show monaxon spicules being pro- 
duced under the same conditions. In Fig. 47 the monaxon actinoblasts still 
remain attached to the gastral epithelium by fine protoplasmic processes, 
though otherwise separated. In Figs. 48 and 49, on the other hand, are 
shown monaxons which show no connection with the gastral epithelium. 
Fic. 50 shows scleroblasts of monaxons stained with Kernschwarz to exhibit 
their cylindrical conformation; only the spicule sheath is seen. 
Fie. 51 shows the migrating basal cells of triradiates similarly stained to 
show their non-cylindrical conformation. 
