EEPORT ON THE TETRACTINELLIDA. 
xlv 
It is indeed difficult while studying this reticulum of connective-tissue corpuscles to 
resist the idea that we are here dealing with something that plays the part of a nervous 
system.” 
In the Challenger sponges I have not yet traced the collencytes into continuity with 
the ectodermal cells, a fact which makes somewhat for Lendenfeld’s theory as to the 
function of the supposed sesthocytes, but I have repeatedly traced them into connection 
with each other, with the choanocytes of the flagellated chambers, and with the myocytes, 
and thus I entertain no doubt as to the general protoplasmic continuity of the cellular 
elements of the sponge. The continuity of the choanocytes of a flagellated chamber with 
each other has already been alluded to (p. xxxviii). 
Scleroblasts. 
Lieberkiilm, Muller’s ArcHv f. Anat. u. Physiol., pts. iv. and v. pi. xv. fig. 22, 1856. 
Carter, Ann. and Mag. Nat. Hist., ser. 2, vol. xx. p. 21, pi. i. fig. 8, 1857. 
O. Schmidt, Zool. Ergebnisse <i Nordenfahrt, p. 120, pi. i. figs. 19-21, 1872. 
Carter, Ann. and Mag. Nat. Hist., ser. 4, vol. xiv. p. 13, pi. xxi. figs. 26, 27, 28, 1874. 
Sollas, Ann. and Mag. Nab. Hist., ser. 5, vol. v. pp. 141, 142, pi. vii. fig. 21 ; p. 256, pi. xi. 
fig. 18; p. 401, pi. xvii. figs. 18-22, 1880 ; vol. ix. p. 159, pL xviii. figs. 12, 17, 18, 1882. 
Polejaeff, Calcarea, Zool. Chall. Exp., pt. xxiv. p. 32, pi, vi. fig. 3, 1884. 
Lieberkiihn and Carter in their classic studies of Spongilla describe the oxeas as 
originating within a fusiform spicule-cell or scleroblast, appearing at first as immeasurably 
thin, hair-like rods lying transversely to the length of the cell. 0. Schmidt describes the 
chelae, sigmas, and orthodragmas of Esperia as formed within a spicule-cell (scleroblast), 
the nucleus of which lies on one side of the orthodragma and in the concavity of the 
chela or sigma. Carter next described the chelae of Esperia segogrophila, Johnston, 
as developing within the embryo in scleroblasts of from 0‘0084 to 0'028 mm. in length, 
and mentions the interesting fact that the chelae, which are anisochelate in the adult, are 
isochelate at their first appearance. The sigmas and toxas also originate in scleroblasts, 
the latter several in one cell, so that at their inception they are dragmas. This is not 
true of all such spicules, however. 
My own paper states that the sterraster of the Geodine sponges originates in a 
scleroblast, the nucleus of which lies in the hilum of the spicule. The young forms of the 
sterraster occur only in the choanosome, where they are present in considerable numbers, 
they are supposed to travel thence into the cortex, where they form a dense spicular 
layer. In this layer none but fully grown spicules are found. I have also shown that the 
large oxeas of Tetilla, Stelletta, and Geodia are formed each within a single scleroblast, 
which persists at least up to the time that the spicule has attained its full growth. 
Polejaeff represents the remains of a scleroblast enveloping a large oxea in a calcareous 
sponge. The examination of the Challenger sponges fully confirms previously obtained 
results, and extends them. 
