REPORT ON THE COPEPODA. 29 



Sub-Class ENTOMOSTRACA, Miiller (Gnathopoda, H. Woodward). 



Order COPEPODA, Milne-Edwards. 



Section I. Gnathostoma, Thorell. 



Family I. Calanid^;, Dana. 



Body elongated, consisting of from ten to twelve segments. Abdomen nearly 

 cylindrical, much narrower than the cephalothorax, and prolonged at the posterior 

 extremity into two more or less cylindrical caudal stylets. Head often continuous with 

 the first segment of the thorax; fourth and fifth thoracic segments often coalescent. Head 

 rarely divided into two segments, but not unfrequently showing an incomplete separation 

 ("cervical suture"). Anterior antennas very long, and composed of twenty-two to 

 twenty-five (rarely fifteen, eighteen, or twenty) joints ; that of the right side in the male 

 often modified for grasping. Posterior antennas large, composed of a basal joint, to 

 which are usually attached two branches, the primary (external) consisting of two, the 

 secondary (internal) of several joints. Mandibles strongly toothed at the apex, palp usually 

 two-branched. Maxillse strong, composed of a more or less quadrate biting portion, 

 which bears numerous curved, setiform, marginal teeth, and a complex, many-lobed palp. 

 Foot-jaws largely developed : anterior pair very broad, inner margins of the basal joints 

 forming wart-like processes, from which spring long ciliated bristles; distal extremity 

 divided into three short joints, which are beset with strong ciliated setse ; posterior pair 

 longer and more slender, basal portion composed of two long and narrow joints, apical 

 portion usually of four to six very small joints. First four pairs of feet two-branched, 

 the outer branches (in the adult) almost always three-jointed. Fifth pair either like the 

 foregoing, or remarkably different, and forming in the male powerful clasping organs, 

 which are unlike on the two sides : those of the female, though often differing from the 

 true swimming feet, always alike on the two sides. A heart is present. Eyes either 

 median and stalked, or paired (lateral) and sessile ; in the latter case often coalescent, 

 and composed of several lenses and pigment-masses : situated usually near the front of 

 the head, but in one genus (Pleuromma) near the base of the foot-jaw of one side only. 

 Sexual organs in the female symmetrical, in the male asymmetrical; ovisac single, borne 

 in front of the abdomen. 



This family includes by far the larger portion of the pelagic Copepoda, being 

 represented abundantly in all seas, from the equator to the poles — or at any rate, as near 

 to those points as scientific investigation has yet been able to extend. 



The overwhelming preponderance of this family in the open sea is at once apparent, 

 when we note that out of the ninety species of free-living Copepoda found amongst 



