The Arenicolidce of Soutli Africa. 13 



indeed, almost obliterate it. The arrangement of the muscles of 

 the wall suggests that the pouch is capable of considerable dilatation. 

 In the intervals between the longitudinal muscle bands there are 

 three large blood-vessels which give off branches, the coelomic 

 epithelial covering of which is composed of cubical or oblong cells 

 containing granules, some of which appear to be yellow and 

 suggestive of chlorogogen granules. The lumen of the pouch 

 opens into the most anterior division of the ccelom in front 

 of the first septum ; the aperture is not a simple pore, but is 

 crossed by a number of muscle fibres. The pouches pass back- 

 wards through the second septum and extend as far as the third 

 one, immediately in front of which their blind ends lie and are 

 generally directed laterally. The enormous size of these septal 

 pouches is the most striking feature of the internal anatomy of 

 this species, and may be given as the principal internal diagnostic 

 character. Comparison with the 'conditions seen in the other 

 species of Arenicola will render this obvious. Septal pouches are 

 not present in A. daparedii and assimilis, those of A. marina and 

 glacialis are small, conical or thumb-shaped structures only 2 to 

 3 mm. long; in A. ccandata and grubii the pouches are finger-like 

 and about 5 to 8 mm. in length, those of the .4. cristata are 

 usually of similar shape and length, but in large American ex- 

 amples they attain a length of 13 mm. The septal pouches of 

 A. loceni are thus twice as large as the largest hitherto found 

 in any other species of Arenicola, and, as already stated, they pass 

 through the second septum and extend backwards to the third, 

 whereas, in all other species, even in large examples of A. cristata, 

 the pouches never perforate the second septum, but lie entirely 

 in front of it. The function of the septal pouches is unknown, 

 but it has been suggested that they aid in the eversion of the 

 " proboscis." 



The powerful retractor muscles of the pharynx (Pn.E.) pierce the 

 first septum ; they arise from the body wall a short distance anterior 

 to the level of the second chaetigerous annulus. 



The second septum (S 2 ) is thin, and, in each of the specimens 

 examined, is pierced by two apertures of considerable size, one to 

 the right and the other to the left of the oasophagus. These two 

 apertures permit the passage backwards of the two septal pouches. 



The third septum (S 3 ) is w T ell developed. In one of the Saldanha 

 specimens, in which it has been examined in detail, this septum is 

 marked on its anterior face with small brown or black spots, each 

 due to the presence of excretory granules in certain groups of cells. 



