158 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
the fauna of the latter locality has been more extensively studied. To my friend, Prof. 
H. 0. Bumpus, director of the Woods Hole station, I wish to express my sincere 
gratitude for many kindly and helpful suggestions during the progress of the work. 
It was thought best to publish the work in its present form in order that it might 
be useful, even as a fragment, in a quantitative determination of the Woods Hole 
plankton soon to be undertaken. The dichotomic table, the synopses of the genera 
of which I have been able to lind representatives, and the salient specific characters 
are translated from Giesbrecht. Simple camera drawings, in nearly all cases from the 
actual specimens, have been introduced for the purpose of facilitating identification. 
The body of a free-swimming copepod is readily separable into two portions, a 
cephalothorax and an abdomen. The former cousists of the head and 5 thoracic seg- 
ments (first suborder, Gymnoplea). The head is often fused with the first thoracic, 
the fourth with the fifth. In the second suborder of the group, the Podoplea , the last 
thoracic segment is drawn into the portion known as the abdomen. The abdomen, 
consisting typically of 5 segments in the male and always of less than 5 in the female, 
may have the number reduced through fusion to 2. or even to a single segment. The 
first abdominal segment bears the reproductive openings and is known as the genital 
segment; the last contains the orifice of the alimentary canal and is called the anal 
segment. This segment bears the f'urca, a pair of appendages each of which is fringed 
with a series of bristles, typically 6 in number, varying in their relative length and 
character. The anterior portion of the cephalic segment is called the front. It 
terminates in the rostrum, which consists of 1 or 2 pointed projections. 
The pairs of appendages which articulate with their respective segments in the 
cephalothorax are in their order: (1) the anterior pair of antennae; (2) the posterior 
pair of antennae; (3) the mandibles; (4) the maxilla? ; (5) the anterior maxillipeds; 
(G) the posterior maxillipeds; (7) four pairs of swimming feet; (8) the fifth pair of 
feet, which are peculiarly modified in both sexes. Appendages 3 to 6 are known 
as the mouth parts. All except the first pair of antennae are typically biramous; i. e., 
each appendage consists of an unpaired 2-jointed basal portion, bearing a 2 or 3 
jointed inner and outer ramus (eudopodite and exopodite) at its tip. One or both of 
the rami may be suppressed. The first pair of appendages, the anterior antennae, 
consists typically of 25 joints, numbered from the base to the tip, but this number 
may be much reduced by fusion. The joints bear modified bristles and sense-hairs, or 
aesthetasks, as Giesbrecht appropriately calls them. In the Gymnoplea each joint 
commonly bears a cluster, consisting of a pair of bristles and an aesthetask. In the 
male one of the anterior antennae (usually the right), or both, may be modified to form a 
geniculating grasping organ. Since nearly all of the appendages are more or less 
flattened, it is convenient to distingush certain regions, with reference to the body 
of the animal, as the anterior and posterior surfaces, inner and outer, and proximal 
and distal margins of the various joints. The number, arrangement, and character 
of the bristles on these different surfaces are of considerable taxonomic value. The 
mouth parts may be provided with bristle-fringed lobes. 
For identification only adult copepods should be selected. This is not always an 
easy matter, as the tow frequently contains immature specimens. The adult male is 
most easily recognized, because in the majority of the genera it has striking secondary 
sexual characters either in the fifth pair of legs or in one or both of the anterior 
antenna:. The adult female is less easily distinguished unless found carrying eggs 
or with spermatophores attached to the genital segment. It is usually necessary to 
