(@COLOGY OF CIRRATULUS TENTACULATUS. 65 
cheetes, after excluding the Errantia, into three classes, according to the 
degree in which they have become adapted to a subterranean existence. 
In connection with this it is interesting to note that it is only in his third 
group, i.e. among those in which the burrowing habit is the rule, that the 
heart-body is present, and that all possess delicate respiratory filaments. 
Bounhiol, to whose paper reference has already been made, belittles the 
value of these processes for respiration, but the point is that they are not 
merely of value as gills pure and simple, but are often the seat of abundant 
cilia which ensure the circulation of water round the body itself. Thus in 
tubicolous forms serious damage to the processes is as dangerous as in Cir- 
ratulide or Arenicolidee. In the Sabellidee, which do not possess a heart- 
body, aeration of the body in the tube is obtained by the perpetual pro- 
trusion and retraction of the branchial crown, and here the branchie or 
tentacles are no longer soft and delicate, but are supported by an un- 
doubted skeleton, whereas in the closely allied Hermellide, e.g. Sabellaria, 
where a heart-body is present, the “ tentacles ” and neuropodial processes 
are again of the delicate type. 
GROUPS POSSESSING A HEART-BODY. 
Famili Habits. Type of branchie. 
Cirratulidee. Permanent burrowers; with Gulls soft, delicate, and fila- 
exception of one boring mentous, capable of great 
form. elongation. 
Terebellide. Forms building tubes of Gills, situated at anterior 
Ampharetide. ! 
Amphictenidee. 
sand or mud. 
Tubicolous. 
end, branched in most 
species, but all soft and 
delicate. 
Gills, situated at anterior 
end, delicate and filiform, 
capable of extension, e.g. 
Pectinaria belgqica. 
Arenicolide. Permanent burrowers. Gills branched and delicate. 
Chlorhemide. Burrowers or inhabitants Gills delicate and filiform. 
of tubes in mud. 
Sternaspidee. Burrowers. Gills delicate and thread- 
like. 
Hermellidee. Tubicolous. Filaments at anterior end 
NEW SERIES,—VOL. XI. NO. l. 
MARCH, 1916. 
are apparently not much 
used for respiration, but 
true branchial processes 
are present on the sides 
of the body. These are 
delicate, unbranched and 
covered with cilia. 
KE 
