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



V. We have adduced additional evidence in favour of 

 Benham's statement that the achjetous region between the 

 prostomium and the first chastigerous segment is formed by 

 the fusion of two segments. The evidence consists (1) in the 

 presence in this acheetous region of one of the segmentally 

 arranged '' giant-cells" in the nerve-cord, immediately behind 

 the point of union of the oesophageal connectives; this cell 

 belonging to the second segment, in which Beuham found a 

 vestigial seta ; (2) in the distinctness of these two segments 

 in the post-larva of A. ecaudata. Consequently the first 

 chfetigerous anuulus of the adult belongs to the third segment 

 of the body. 



VI. The neuropodial crotchets undergo considerable 

 changes in form during the life of a worm. The rostrum, which 

 in chsetse from young specimens is at right angles to the shaft, 

 in later formed ch^tas makes a considerably greater angle, 

 the angle increasing with the age of the worm. Concurrently 

 there is a reduction in the size of the teeth of the ch^tge, and 

 finally they disappear. We have confirmed the observation 

 of Mesnil that a crotchet, identical in form with those of the 

 neuropodium, occurs in the notopodium of each of the last six 

 setigerous segments of the post-larva of A. ecaudata. The 

 crotchet is soon lost from the notopodium, and henceforward 

 only capillary setae are found there. 



VII. The heart-body, though absent in A. cristata and 

 A. Claparedii, occurs in A. marina, A. ecaudata, and A. 

 Grubii. It is absent in young specimens, and does not 

 develop until the animal is two or three inches in length. In 

 later stages it arises as finger-like ingrowths formed by 

 proliferation of the cells of the wall of the ventricular part 

 of the heart which connects the gastric vessel or sinus on 

 each side of the stomach with the ventral vessel. These 

 proliferations are very soon followed by invaginations which 

 carry the endothelium, the muscles, and the peritoneal lining 

 of the cardiac wall inwards. From the inner ends of these 

 short invaginations further proliferation takes place, so that 

 ultimately the cavity of the heart is reduced to a series of 



