460 r. W. GAMBLE AND J. H. ASHWORTH. 



side (1) small vessels from the oesophageal pouches (except in 

 A. Claparedii), (2) vessels from the anterior nephridia (see 

 figs. 26, 30, 44, 45), (3) on reaching the third diaphragm a 

 vessel from the third chsetigerous sac and body-wall, and (4) 

 on reaching the second diaphragm, one from the second 

 chaetigerous sac and body-wall. The dorsal vessel runs for- 

 ward, pierces the first diaphragm, and then breaks up into 

 capillaries, supplying the buccal muscles, prostomium, and 

 otocysts. 



The blood from these parts is collected into capillaries 

 which unite to form the ventral vessel, which, soon after its 

 origin, gives off a median vessel to the first diaphragm and, 

 when present, its pouches : while just behind this, in A. 

 cristata and A. Claparedii, it gives off a pair of vessels 

 to the second setal sacs and body-wall. A little further back 

 it supplies a median branch to the second diaphragm and 

 nerve-cord, and another to the third diaphragm, the cord and 

 first nephridium (and in A. Grubii and A. ecaudata a 

 median vessel to the cord about the level of the first 

 nephridium). From this point the ventral vessel as it pro- 

 ceeds backwards supplies the chaetigerous sacs, body-wall, 

 nephridia, and gills (if present) by large segmentally arranged 

 branches. The first and second nephridia of A. Grubii and 

 A. ecaudata do not receive a branch from the ventral vessel. 



The difference of opinion which has existed on the subject 

 of the nature of the blood-supply of the stomach and intestine 

 appears susceptible of a very simple explanation. The earlier 

 writers described this supply as a plexus of minute vessels, 

 later authors as a continuous sinus, only parts of which are 

 visible between the chlorogogenous areolae. Benham (1893), 

 however, showed that in the post-larval stage of A. marina 

 there was a feebly developed plexus, but no sinus, and we 

 are able to show by the examination of a large number of 

 specimens of this species, that up to a length of 50 mm., or 

 even more, the plexus increases, and only here and there 

 (e.g. in the walls of the oesophageal pouches) fuses to form a 

 '^ sinus." As the lugworm increases in size this formation of 



