No. 38] DEVELOPUENT OF MARINE: SPONGES. 301 
those I watched did not develop any further than the stage 
shown in Fig. 37. 
"In his memoir on Spongilla, Gotte (6) claimed that the entire 
ectoderm of the larva was lost, the inner mass of cells giving 
rise to all the layers of the adult. This account was opposed 
to the earlier one of Ganin (7) who described the larval ecto- 
derm as retained and becoming the ectoderm of the adult. In 
his preliminary paper on the development of Spongilla, Maas 
(15) stated that the larval ectoderm was not thrown off, but 
after loss of cilia and gradual flattening became the thin mem- 
brane-like ectoderm of the adult; and the excellent series of 
figures given in his later paper (14) retrace the process step by 
step. Some of the older writers, Metschnikoff (11) and 
Schmidt (22) described a partial or complete loss of the larval 
ectoderm in several silicious sponges during the metamorphosis; 
Barrois (1) believed that in his Desmacidon and_ Isodyctia 
larvae, the ectoderm was partially lost; and among the more 
recent investigators, Marshall (18) describes a partial loss of 
the ectoderm in Reniera filigrana. On the other hand, the 
flattening of the larval ectoderm and its transformation into 
the adult covering, has been observed not only in the case of 
Spongilla, but in other carefully studied silicious sponges : in 
Chalinula, Keller (10), and Myxilla, Vosmaer (34). For the views 
of Yves Delage and Maas on the relation of the larval ecto- 
derm to that of the adult in Esperia, reference may be made to 
pp. 317-319. It seems to me that the alleged cases of total or 
partial loss of the larval ectoderm (ectodermic hernia) so com- 
pletely lack the requisite detailed proof, that none of them can 
be accepted. In all such cases it is probable that the ectoderm 
is not lost, but is flattened into an extremely thin membrane. 
Ectoderm. —In the flat epithelium into which the columnar 
ectoderm changes, the separate cells are at first easily made out 
(see Pl. XVII, Fig. 36, longitudinal section of a larva like that 
shown in Fig. 28). When the metamorphosis is complete, 
however (see Pl. XVII, Fig. 38, entire vertical section through 
recently attached sponge, and Pl. XVII, Fig. 44, ditto through 
an older sponge), the ectoderm on both upper and lower surfaces 
forms a very thin membrane, in which nuclei are discernible 
