718 HaroLp HEATH, 
of the chitons and it is possible that we have to do with an 
excretory apparatus. The membrane bounding the lateral sinuses 
is penetrated by numerous minute pores so that the blood readily 
passes into the visceral cavity. 
In the posterior end of the body the blood from the pedal and 
visceral sinuses unites and at once passes into the afferent branchial 
vessel which holds a position below the ventral gill retractor and 
passing through the gill lamellae enters the efferent vessel occupying 
a corresponding position above the dorsal gill retractor. From here 
it passes backward and enters the hinder end of the heart thus 
completing the circulation. 
Compared with other solenogastres the corpuscles are remarkably 
few in number, being not more than one third as abundant as in 
Proneomenia hawaïiensis. In living specimens the blood is distinctly 
red, the head and especially the gill region having a pinkish hue 
but whether the haemaglobin is carried by the corpuscles or plasma 
I do not know. The general appearance of the blood cells is shown 
in Fig. 20. In a considerable number of cases the nucleus is distinctly 
bilobed as though in the first stages of amitotic division. 
The main features of the nervous system may be determined 
from specimens treated with the ordinary stains but the finer details 
such as some of the commissures and even the more important perves 
arising from the larger ganglia are absolutely invisible after such 
treatment. On the other hand these elements appear with considerable 
clearness in specimens fixed in Vom Ratn’s fluid which is thoroughly 
washed out in 70°), alcohol; and it may be added that all the 
other tissues of the body are finely preserved and clearly defined. 
The brain, situated in the usual position, is very clearly bilobed 
in form and is closely associated with five pairs of ganglia that 
almost cover its anterior and ventral faces (Fig. 7). Fibres from 
the brain enter at least eight of these masses each of which 
originates another great nerve that makes its way to the buccal 
sensory plate. It seems remarkable that this latter structure should 
be supplied with ten nerves and these of relatively huge size and yet 
there are no indications that the fibres have any other destination. 
More posteriorly the connectives from the pedal, lateral and labio- 
buccal ganglia pass into the brain. As is shown in Fig. 7 the 
pedal and lateral connectives unite a considerable distance from the 
brain while the labio-buccal fibres join more dorsally. 
The pedal cords hold the usual position along the ventral side 
