C6 EF. W. FLATTELY. 
The above table shows considerable similarity in the nature of the gills 
and habitat among the species of those families which possess a heart- 
body. The majority are burrowers, permanently subjected to pressure, 
and even in the tubicolous forms, seeing that they must often become 
sanded up (for instance, by wave shock when the tide is rising), the 
possession of a heart-body cannot but be advantageous in preventing re- 
gurgitation of the blood to the dorsal vessel, keeping the branchial pro- 
cesses turgid, and generally counteracting the effects of varying pressure. 
As a proof of this we note that the greatest development of the heart-body 
occurs in just those groups where burrowing habit and branchial develop- 
ment are carried to their greatest extent. 
It is perhaps advisable to point out here that any mechanical function 
which is suggested on behalf of the heart-body is only regarded as 
secondary. There seems hardly any doubt that in the heart-body we are 
dealing with a structure the original function of which was almost, if 
not entirely, organic. 
It may be urged that, according to this theory, one might reasonably 
expect to find the development of a heart-body in those other groups of 
M. Bohn’s where the burrowing, free-swimming, and crawling habits are 
combined, e.g. in the Aphroditide, Phyllodocide, Nephthydide, Gly- 
ceridx, EKunicidee, Ariciide. In these groups, however, apart from the 
fact that, owing to their semi-active habits, the danger of asphyxiation 1s 
considerably reduced, the branchial processes themselves are in most cases 
effectively protected by the great development of the parapodia and 
chete. This is excellently exemplified by the condition in Nephthys, 
where the sickle-shaped gill is situated between the strongly developed 
lobes of the parapodia and their lengthy chete. 
As we pass to the consideration of forms with more and more pre- 
dominantly burrowing habit we note the concurrent reduction in size of 
the cheete, for, useful as they undoubtedly are in swimming and crawling, 
they can only bea hindrance to progress in and through sand. The bristles 
acquire more and more the character of short hooks, enabling the animal 
to grasp the side of its burrow, and, if the gills are to be retained, a new 
method of protection must be adopted. 
Merion or Frepinc.—-I will now examine the specialised method of 
feeding in Cirratulus in more detail. Unlike its congener in the same 
habitat, Arenicola, Cirratulus does not live by passing sand through the 
gut ; selection of the nutritive organic particles is made outside the body. 
The excreta are green in colour, and the worm’s diet would seem to consist 
of algal spores, fragments of decaying alge, diatoms, and general organic 
debris. Jn preparing the worm for sectionising no special precautions 
were taken to ensure the emptying of the gut, and the razor did not suffer. 
