728 HAROLD HEATH, 
Rhopalomenia. In the neighborhood of the openings of the ventral 
salivary glands they connect with ganglia') which in turn are very 
closely associated with four commissures. Comparing these last 
named fibres with similarly related structures in the chitons and 
the prosobranchs it is evident that they correspond to the labial, 
subradular and dorsal and ventral (anterior and posterior) buccal 
commissures. In Proneomenia, where a well defined radula is present, 
it is comparatively easy to homologize these but in Rhopalomenia 
where this organ is the merest diverticulum and all of the ventral 
commissures in close proximity to it the task is most difficult. 
In Proneomenia the subradular connectives spring from the inner 
side of the labial nerve masses and unite with ganglia in close 
proximity to the sensory areas. Their relations are therefore typical. 
For Rhopalomenia I have figured a similar state of affairs, though 
well defined subradular organs are absent. The dorsal buccal 
commissure arises on the labial connectives some distance anterior 
to the labial ganglia while the ventral buccal commissure arises 
from the ganglia themselves and passes dorsal to the radula in 
characteristic fashion. In Rhopalomenia the dorsal commissure 
originates from the labial connectives but relatively close to 
the labial ganglia while the ventral commissure, of relatively large 
size, originates from the posterior borders of these nerve masses. 
In this genus a third ventral commissure exists which I consider 
corresponds to the labial since it gives rise to two symmetrical 
nerves which soon break up into a large number of fibres passing 
into the pharyngeal wall where they soon become lost to view after 
passing toward the mouth somewhat as in the prosobranchs. In 
Proneomenia a nerve arises from each labial ganglion, and is also 
distributed to the pharyngeal wall but as each courses through 
great masses of muscles I have not to been able to follow it far nor 
determine if it is in reality part of a true commissure. 
The great theoretical importance attaching to the relations 
of the gonad, pericardium and coelomoducts have been the subject 
of many discussions from the advent of HuBrecars beautiful 
paper on Proneomenia sluiteri down to the present time. Several 
authors have called attention to the resemblance to the annelids in 
this respect and have noted the modified condition in the majority 
1) In both species of solenogastres the buccal ganglia are not sharply 
differentiated and are probably partially fused with the labial. 
