104 THE FRESH- WATER CRAYFISH— THE CAPE CRAWFISH 



(/) The digestive glands or " liver," a yellowish bilobed mass of coiled tubes, 



lying in the thorax on each side of the alimentary canal. 

 (g) The long and straight intestine, along the mid-dorsal line of the body, 



and between the extensor and flexor muscles in the abdomen. 

 (h) The gonad (testis in male or ovary in the female), portions of it on each 



side of the intestine. Note the long and coiled vasa deferentia (or 



short oviducts in the female). 

 (i) The heart lying within the pericardiiim in the dorsal region of the thorax. 

 (j) The median ophthalmic, antennary, hepatic, and superior abdominal 



arteries. 



A. The Vascular System (part). 



Examine the heart and note that it has three pairs of apertures or ostia — 

 a pair on the dorsal surface, a pair on the ventral surface, and a pair placed 

 laterally. [In Jasus there are two pairs of ostia placed dorsally.] The heart is 

 attached to the walls of the pericardial sinus or pericardium by strands of con- 

 nective tissue. From the anterior end of the heart the following vessels arise : — 



(a) The single median ophthalmic artery, which passes over the gizzard and 



then branches into two ophthalmic arteries, one to each eye. 



(b) The pair of antennary arteries, one passing over the " liver " on each 



side and supplying the antennae. 



(c) The pair of hepatic arteries arising one on either side of the heart between 



the ophthalmic and antennary artery, and passing down into the 

 substance of the " liver." 



From the posterior end of the heart there arises the superior abdominal 

 artery, which passes backwards on the dorsal surface of the intestine to the tail 

 region. It supplies each segment of the abdomen by a pair of smaller arteries. 

 Just posterior to the heart the superior abdominal artery gives rise to a sternal 

 artery, which passes vertically downwards to the ventral region of the cephalo- 

 thorax. Sever this artery at its origin, and lay it aside for further examination. 



B. The Alimentary System. 



The mouth is an elongated opening below the head. It is bounded in front 

 by a wide upper lip or labrum, on the sides by the mandibles, and behind by the 

 paragnatha, which resembles the first maxilla. A short wide gullet leads up- 

 wards and forwards from the mouth to the large stomach or gizzard, which is 

 divided into two portions, the anterior cardiac chamber or gastric miU and the 

 smaller posterior pyloric chamber. From this the short mid-gut or mesenteron, 

 which has a dorsal pouch or caecum, leads into the long intestine, which ends 

 at the anus situated beneath the telson. The gullet and gizzard represent the 

 fore-gut or stomodaeum ; and the intestine is the hind-gut or proctodaeum. 



Note the large " liver," which consists of two digestive glands, a big yellow- 

 ish mass of tubules, Ijdng on each side of the pyloric stomach. Ducts from the 

 tubules unite into an hepatic duct opening into the mesenteron on each side. 



Cut through the gullet or oesophagus and the intestine (near the anus), and 

 carefully remove the alimentary canal with the attached " liver." Remove the 

 " liver " on the left side, and make a side-view sketch of the alimentary canal. 



Remove the stomach or gizzard and open it along the ventral wall. Note 



