64 THE CRUSTACEA 



The short rectum opens on the ventral side of the furca in 

 MyodoeopiT, but on the dorsal side in the Cyprididae and allied 

 families. 



Circulatory System. — A heart is present only in the Myodocopa 

 (Fig. 38, //). It is placed near the dorsal surface just above the 

 mandibles, and has one pair of lateral ostia and an opening in 

 front tlirough which the blood is expelled. No definite vessels 

 exist, but a network of blood-channels is found in the shell of the 

 Cypridinidae. The blood is coloured red in Krithe. 



Respiratory System. — In the majority of Ostracodathe respiratory 

 function is probably discharged by the general surface of the body 

 and limbs and by the inner surface of the shell. The so-called 

 " branchial appendages " found on the various limbs serve to 

 keep up a current of water within the shell. Only in the genus 

 Asterope, and less distinctly in one or two species of Cypridimi, are 

 definite branchiae found. These are lamellar appendages attached 

 to the dorsal surface of the posterior part of the body. Seven 

 pairs are present in Asterope. 



Excretory System. — Little • is known regarding the excretory 

 system of the Ostracoda. " Segmental " organs in the form of 

 small sacs lying at the bases of the ambulatory legs are described 

 in Paradoxostoma and Bairdia. It is doubtful whether they open to 

 the exterior. In Cypris a gland lying in the labrum and opening 

 on the first segment of the antenna and a second gland opening on 

 the basal segment of the third post-oral appendage (maxilla ?) have 

 been described. 



Glands. — As already stated, dermal glands are frequently found 

 in the valves of the shell. In some Cypridinidae their secretion 

 serves to agglutinate the sand in which these animals burrow, and 

 in some cases to form definite tubular dwellings. In the Halo- 

 cypridae the glands are most numerous near the edge of the 

 anterior part of the shell, and it is stated that their mucus-like 

 secretion serves to entangle food-particles and is then swallowed. 

 Specially large glands openijig near the margins of the valves 

 anteriorly are found also in some other Ostracoda, and, from their 

 position, suggest a comparison with the " fronto-lateral glands " 

 similarly situated in the " Cypris-larva " of Cirripedes. Glands are 

 sometimes found in the labrum (Cypridinidae and Cyprididae), and 

 are believed, in Pyrocypris, to produce a luminous secretion. The 

 spinning-glands of Cytheridae have already been mentioned. 



Musculature. — The adductor muscle (Fig. 38, S.M) runs between 

 the valves of the shell on the ventral side of the alimentary canal. 

 In some Ostracoda, especially in Cyprididae, a tendinous plate is 

 found below the anterior part of the alimentary canal, serving for the 

 attachment of the mandibular and maxillary muscles. It is worthy 

 of note that the adductor muscle does not share in its formation. 



