324 THE CRUSTACEA 



rectum. A pair of glandular sacs lying in the telson on either side 

 of the anus have been observed in the larva and perhaps open into 

 the rectum. It is not known whether they persist in the adult. 



The digestive gland is very voluminous. It forms a compact 

 mass of glandular tissue closely investing the intestine throughout 

 the whole of its length and sending out on each side a series of 

 diverticula segmentally arranged corresponding to the last three 

 thoracic and the abdominal somites, and it finally terminates in a 

 series of ramifying processes, which radiate throughout the telson 

 and even penetrate into the peduncles of the uropods. It was 

 formerly stated that this gland originated as a series of segmentally 

 arranged diverticula from the alimentary canal, and that it com- 

 municated with the intestine by a series of apertures on each side 

 throughout its whole length. It appears, however, that this is not 

 the casd, but that the gland-follicles open into a pair of longitudinal 

 ducts which unite to enter the dorsal part of the pyloric chamber 

 of the stomach. 



Ckmlatory System. — The Stomatoi)oda are unique among the 

 Eumalacostraca in possessing an elongated tubular heart extending 

 through nearly the whole length of the thoracic and abdominal 

 regions, and provided with numerous segmentally arranged pairs of 

 ostia. 



The details of the circulatory system have been most fully made 

 out in the later larval stages by Claus, but the older accounts of the 

 adult by Audouin and Milne-Edwards and by Duvernoy, though 

 incomplete, show that no very profound changes occur in the adult. 

 The anterior part of the tubular heart, lying in the maxillary region, 

 is dilated, and its dorsal wall is perforated by a pair of large ostia. 

 Anteriorly, it gives off a median aorta which sends branches to 

 brain, eyes, antennules, and antennae, and a pair of antero-lateral 

 arteries to the carapace and viscera. Behind the region of the first 

 thoracic appendages the heart is of uniform diameter, and bears 

 twelve pairs of ostia and fourteen pairs of lateral arteries arranged 

 for the most part in correspondence with the segmentation of the 

 body. Posteriorly the heart is continued into a short caudal aorta 

 running into the telson. 



From one of the lateral arteries of the first pair there originates 

 an unpaired arteria descendens, which pierces the ventral ganglionic 

 mass between the first and second thoracic ganglia, to communicate 

 with a subneural artery which underlies the nerve-cord throughout 

 its Avhole length. This subneural artery further communicates 

 with the heart by means of its lateral branches, which anastomose 

 in the various somites, sometimes on one side, sometimes on both, 

 with l^ranches of the lateral arteries. Capillary networks of great 

 complexity are formed in the brain and in the ventral ganglia. A 

 point of some interest is the unsymmetrical origin of the arteries 



