744 J. n. ASHWOKTH. 



diaphragmatic pouches, and in some species they attain a 

 large size, e.g. in A. cristata they may reach a length of 

 12 mm. Many of the blood-vessels which cross the coelom 

 obliquely to the nephridia and gills are provided with a verj- 

 obvious connective-tissue strand or band, which graJually 

 increases in size in the posterior segments of the gill region, 

 forming in the last two or three segments of this part of the 

 body an almost complete septum supporting the afferent and 

 efferent branchial vessels. There are well-developed caudal 

 septa. 



Alimentary Canal. — The most striking feature of the 

 internal anatomy of A. assimilis is the presence of multiple 

 oesophageal pouches. These are placed on the sides of the 

 oesophagus, just behind the third diaphragm. There are in 

 each of two specimens six, and in another eight, pouches on 

 each side. The anterior pair is long — 12 mm. in one speci- 

 men, 17 mm. in another, — and each of them is usually swollen 

 at or near its anterior free end, having a club-shaped appear- 

 ance. Their abundant blood-supply is evidenced by the 

 network seen in tlieir walls. In the contracted condition 

 these anterior pouches are digitiform structures with a some- 

 what moniliform appearance. The smaller posterior glands 

 are from 1 mm. to 4 mm. in length, and are pear-shaped or 

 oval sacs with rather thicker walls. As in other Areni- 

 colidas, the cavity of each pouch is partially subdivided by 

 numerous septa produced by infolding of the wall; each 

 septum, therefore, is composed of two lamelltB of glandular 

 epithelium, between which is a cavity filled with blood. Tlie 

 partitions are very obvious in the smaller pouches, and in 

 the larger pouches when in a contracted condition; but when 

 these are fully distended the septa become mere ridges on 

 the inner wall of the pouch. In the presence of nudtiple 

 oesophageal pouches A. assimilis conforms to another of 

 the features hitherto considered to be peculiar to A. 

 claparedii, as in all other species of Arenicola in which 

 the pouches are known there is only n single pair.^ In otlier 



' KhlcTS (I'JOl, p. 177) states that the gut- of A. assimilis a^rt-rs willi 



