376 JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, Vol. XVIII. 



passage, the sternal sinus, in which the nerve cord and the two 

 branches of the sternal artery lie. In the thorax the sternal sinus 

 sends a vessel to each gill, which runs up the outer side of the gill- 

 stem as an afferent (Latin affere, to bring to) gill vessd. In the gill 

 the blood is only separated from the water by a thin diffusible 

 membrane, so that an interchange of gases between the blood and 

 the water readily takes place. Carbonic acid is given off, oxygen is 

 taken in, and the purified blood is carried by an efferent (Latin effere, 

 to carry away from) vessel or vein on the inner side of the gill-stem. 

 The efferent veins from the twenty-one gills unite into six larger 

 vessels, the branchio- pericardiac canals, which pour the blood into the 

 pericardiac sinus, whence it enters the heart during diastole, and so 

 the circulation is completed. 



The efferent and branchio-pericardiac vessels can readily be 

 injected with ink from a finely pointed medicine dropper, by cutting 

 across the base of a gill and injecting the inner vessel. The course 

 of the circulation in these vessels may also be demonstrated by 

 blowing in air from a blow pipe. The air can be seen to bubble into 

 the pericardial sinus if the sinus be filled with water. 



The General Relations of the Viscera. 



Remove the whole carapace and the terga of the abdomen with the 

 underlying integument. Also the extensor muscles of the abdomen. 



Note the alimentary canal, a straight tube near the dorsal surface 

 running the whole length of the body. Throughout the greater 

 portion of its length it is brownish in colour and about as thick as a 

 crow-quill. In front it is much enlarged to form the stomach, which 

 fills the greater part of the head. Below the " cardiac area" of the 

 carapace you find the heart, a dirty white or slightly yellowish, some- 

 what translucent organ, lying dorsal and posteriorly to the stomach in 

 the -pericardial cavity. Note the dorsal abdominal artery, a translucent 

 tube running from the posterior end of the heart along the dorsal 

 surface of the hind gut, also the three arteries running from the 

 anterior part of the heart. 



The ao m ids (Gr. gone, seed or reproduction) or reproductive glands, 

 lying below a thin membrane, the floor of the pericardial sinus, and 

 partly covered by the heart. They vary in size and colour with the 

 seasons. In the male the testes, two long white masses, joined near 

 the middle by a transverse median piece. In a full grown, lusty 



