64 HI. J. Clark.—Tubularia Not Parthenogenous. 
excessively thin, longitudinally fibrillated muscular layer be- 
ween the outer and inner walls of the stem, disc, tentacles, and 
branching stems of the genitalia; and whenever the latter pul- 
lulate to form a genital sac, a medusoid, all the cellular and mus- 
cular elements enter into the operation, and thus there arises at 
first a highly contractile, triple walled hernia, the outer wall of 
which consists of a single stratum of broad cells, each containing 
~ a large nucleus; the middle wall, or stratum, forms the muscular 
layer; and the innermost wall is made up of a single layer of 
latter also becomes globular. Surrounding this space we have 
on one side the outer wall at the end of the bud and on the 
other side, the inner wall, lined by the muscular layer, crane 
stratum which is the ovigerous layer. 
Only one step more is now required to perfect the morpholo- — : 
gical plan of development of this organ, and that is brought ® 
