No.44] ANORTH-AMERICAN INVERTEBRATES. 483 
confined to the ventral surface and are there often arranged in 
three broad longitudinal series. Many holothurians have a 
pair of long, much-branched outgrowths of the wall of the 
cloaca lying in the body cavity, one on each side of the intes- 
tine. These serve for excretion, and perhaps for respiration, 
and are called the respiratory trees. Their presence or absence 
is of importance in classification. The stomach and anterior 
Fics. 5-11 
4 A radial and interradial piece of the calcareous ring of Synafta inhærens (O. F. Müll). x 4s. 
e same of Syzapta roseola (Verr.). x 45. 
7. À radial and two interra dial pieces of a “calcareous ring with posterior prolongations.” 
one briareus (Less. NS. 
8. The same of a “ calcareous ring without posterior prolongations." Thyone suspecta Ludw. x 3. 
9- A dendroid tentacle. Cuca ia punctata Ludw. x 3. 
10. A > ss 3 
Agent. hence. 
Portion of the intestine are held in position by a thin membrane 
attached to the body wall in the mid-dorsal line, and called the 
orsal mesentery. In this lies the genital duct, and the geni- 
tal glands lie in groups or tufts either on one or both sides 
of it. In some holothurians the long radial muscles are divided 
anteriorly, one-half continuing attached to the body wall and 
Serving merely as a longitudinal muscle, while the other is free 
