REVIEW OF SPENGEL’S MONOGRAPH ON BALANOGLOSSUS. 397 
It is the most differentiated genus, and has the following 
characters : . 
The proboscis has the typical form, being about one and a 
half times as long as broad; the collar is as long asitis 
broad, and the crura of the skeleton only reach 
through its anterior half. 
The tongue-bars of the inner gill openings are 
bound to the sides of the sacs by synapticula, as shown 
in Pl. 29, fig. 13a. We see that whereas in Amphioxus the 
synapticula run straight across the gill-slit, and are, according 
to Professor Spengel, secondarily fused with the tongue-bar, in 
Ptychodera they are at different levels on opposite sides of the 
tongue-bar. 
The body in the branchio-genital region is produced into 
lateral flaps (Pl. 30, figs. 2 and 3), the genital wings, 
which contain a large portion of the gonads. 
The digestive region of the gutis produced into 
papilla-like diverticula, which give rise to protrusions of 
the dorsal surface of the animal. These liver saccules are 
distinguished by the green matter which their cells contain ; 
they open by narrow slits into the gut, and never contain food 
material. 
In the branchio-genital region behind the gill-sacs we find 
the trunk celom divided into dorsal and ventral 
chambers by oblique septa. Each chamber contains a fork 
of the bifid gonad (see Pl. 29, fig. lla). These bifid gonads 
open along the line of insertion of this lateral septum. If we 
trace the septum backwards, it ends in a free edge at the com- 
mencement of the liver region; traced forwards towards the gill 
region, it becomes inserted on the skin at both ends; in other 
words, the dorsal chamber becomes displaced from the middle 
line by a median upgrowth of the ventral chamber, as shown 
in fig. 114. In the gill region the dorsal chamber becomes a 
small space containing no part of the gonad, and half choked 
with muscular and connective tissue (Fig. 5). From the fact 
that the dorsal chamber contains no radiating muscles, and that 
the lateral septum ends in free edge behind, but fuses com- 
