THE AMPHIPODA 235 



region is similar in both cases, the ventral sinus sending blood into 

 the appendages, from which it is returned to the pericardium by 

 the centripetal sinuses ; the ventral sinus in Amphipoda receiving, 

 however, arterial blood directly from the posterior aorta. In the 

 thorax the course of the circulation is very different. 



In the Isopoda the appendages receive blood directly from the 

 heart by means of the lateral thoracic arteries and return it to the 

 ventral or lateral thoracic sinuses ; in the Amphipoda, on the other 

 hand, the limbs with their branchial plates receive blood from the 

 ventral sinus and return it directly to the pericardium by the peri- 

 cardial vessels. The ventral sinus of the Amphipoda, however, 

 does not wholly correspond to the ventral or lateral sinuses of the 

 Isopoda, but, since it receives arterial blood both anteriorly and 

 posteriorly from the aorta, represents in part also the sternal 

 system of arteries in the last-named group, while the homologues of 

 the thoracic afferent pericardial vessels of the Amphipoda are to 

 be found in the blood-stream which enters the pericardium of the 

 Isopoda through the minute apertures at its anterior end. 



Excretory System. No trace of a maxillary gland has been 

 recognised in any Amphipod. The antennal gland, on the other 

 hand, is rarely, if ever, wanting. It has been most fully studied 

 in certain freshwater Gammaridae, where it presents the usual 

 divisions of end-sac, convoluted tube, and duct, the latter being some- 

 times dilated into a vesicle. The gland is usually contained within 

 the first segment of the antenna, and its external aperture is at 

 the tip of a conical or spinifornv process of the second segment. 

 " Coxal glands " are described as present in all the thoracic and the 

 first three abdominal appendages of Gammarus. They consist of 

 small groups of cells, without duct or opening to the exterior, 

 rendered visible in the living animal by feeding with carmine. 



Dermal Glands. In many Amphipoda there are found groups 

 of unicellular glands lying in the thoracic appendages and opening 

 by fine ducts at or near the extremity of the limb. Among the 

 Gammaridea such glands are well developed in the Photidae, 

 Aoridae, Amphithoidae, Jassidae, Corophiidae, and some of the 

 allied families, where they are confined to the fourth and fifth 

 thoracic appendages, lying mainly in the basipodite and connected 

 with a duct which opens on the tip of the claw. In the Ampelis- 

 cidae similar glands occur but are more widely distributed on the 

 other appendages of the body. In all the families named the 

 glands secrete a cementing material which is used in building up 

 with particles of mud or sand or fragments of weed the cases or 

 tubes in which the animals live. In the Talitridae, which burrow 

 in sand, glands of similar structure are scattered over the surface 

 of the body and appear to secrete a mucinous substance which lines 

 the burrows. Glands of very similar structure to those just 



