ANATOMY OF ARENICOLA ASSIMILIS. 769 



The specimens were dug I'ruui the sand iu Whale Sound^ 

 Stanley Harbour, during the early months of this year (1902). 

 They are respectively 187, 185, 135, 128, and 121 mm. long. 

 Each has nineteen chaitigerons segments, the seventh of 

 which bears the first and invariably small pair of gills.^ The 

 other external characters, e. g. the prostomium, aunulation, 

 etc., agree exactly Avith those of the Otago specimens, while 

 internally the agreement is scarcely less perfect. In the two 

 specimens dissected there are six pairs of uephridia opening 

 on the fourth to the ninth segments. The first uephridium 

 is small, and its nephrostome is on the anterior face of the 

 third diaphragm. The edge of the ventral lip of the larger 

 uephrostomes is thrown into numerous folds or frills, as 

 figured (see fig. 1 7). The vascular system agrees exactly with 

 that of the Otago specimens. 



There are multiple oesophageal glands to the number of 

 twelve or thirteen on each side, the anterior ones digitiform 

 or club-shaped, the others pyriform or ovoid. There are no 

 pouches on the first diaphragm. 



The only feature of an unusual character in the body of the 

 animal is the presence of a partial septum one segment 

 behind the third diaphragm. This structure is homologous 

 to the septa met with iu the posterior branchial region of 

 this and other Areuicolidsc. It is a membrane supporting both 

 the afferent and efferent vessels to the second pair of 

 nephridia, and is nearly 3 mm. across in its widest part. It 

 is not so extensive as the third diaphragm (which iu the 

 same specimen is over 6 mm. across), as it does not reach 

 either the dorsal or the ventral body-wall. It may bo 

 regarded as merely an exaggeration of the supporting 

 strands which are usually present in other species alongside 

 either one or both of the vessels to the nephridia (see, for 

 example, A. grubii, Gamble and Ashworth, 1900, pi. xxvi, 

 figs. 53, 54). 



The two specimens examined are females which have 

 probably spawned, as only a very few ova are present iu the 

 ' Iu one specimen the true first gill is absent on the right side. 



