12 ARKIV FÖR ZOOLOGI. BAND 7. N:0 5. 



The strong first septum (S^) bears two enormous back- 

 wardly-directed pouches (S. P.), much larger than tbose of 

 any other species. In tbe three specimens examined these 

 pouches are 25 to 26 mm. long; they are about 3,5 mm. in 

 diameter in front but taper gradually towards their blunt 

 posterior ends. The wall of the pouch consists of four layers; 

 externally and internally there is a very thin film of coelo- 

 mic epithelium, between which are two series of muscles. The 

 outer layer of muscles is about 0,5 mm. thick and its fibres 

 are chiefly circular in direction, the inner one consists of a 

 series of stout longitudinal bands, similar to those seen in 

 sections of the body wall, which project into the lumen of 

 the pouch and, 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 longi- 

 tudinal 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 gran- 

 ules, some of which, at least, appear to be yellow and sug- 

 gestive of chlorogogen granules. The lumen of the pouch 

 opens into the most anterior division of the coelom 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 

 backwards 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 

 these septal pouches is the most striking feature of the inter- 

 nal anatomy of this species and may be given as the prin- 

 cipal 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. claparedii 

 and assimilis, those of A. marina and ^/acia/z<s are small con- 

 ical or thumbshaped structures only 2 to 3 mm. long; in 

 A. ecaudata and grubii the pouches are finger-like and about 

 5 to 8 mm. in length, those of the A. cristata are usually of 

 similar shape and length, but in large American examples 

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

 loveni 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 



