ANATOMY OF ARENICOLA ASSIMILTS. 761 



Zealand specimens is a matter of considerable difficulty. In 

 tlie number of cha3tigerous segments and position of first gill 

 tliey resemble A. marina and A. claparedii, but the pro- 

 stomium is more nearly like that of the former. Internally 

 there are four characters, two of which are in agreement with 

 those of A. marina and in contrast to those of A. claparedii, 

 sind two are vice versa — (1) the number and position of the 

 nephridia and the presence of open otocysts, and (2) the 

 presence of multiple oesophageal glands and the absence of 

 pouches on the first diaphragm. The absence of otocysts in 

 A. claparedii is so remarkable and characteristic a feature 

 that their presence in the Otago specimens, taken in con- 

 junction with the important differences in the number of 

 nephridia and the form uf the prostoujium, is sufficient to 

 exclude the southern specimens from Levinsen's species. 

 While their rehitionship with A. marina rests on a strongei" 

 basis, the internal differences are too important to be passed 

 over, and one must look elsewhere for a nearer ally. 



Throughout the description of the anatomy of the New 

 Zealand specimens it is striking how frequently a perfect 

 agi-eement occurs between them and A. assimilis. Their 

 prostomia are practically identical, and they further agree 

 in almost every internal character — the number and position 

 of their nephridia, their oesophageal glands, the absence of 

 pouches on the first diaphragm, the form and structure of the 

 brain, the large size of their open otocysts and of their ova. 

 The only differences are externally in the number of seg- 

 ments and the position of the first gill, and internally in the 

 vessels of the seventh segment and in the nature of the 

 otoliths. It is a question whether these differences are uf 

 sufficient importance to justify the separation of the New 

 Zealand specimens as a distinct species. 



The form of the otcjliths is certainly very dill'ercnt. In 

 A. assimilis the}'' are rounded, and consist almost entirely 

 of a substance secreted by the cells in the wall of the 

 otocyst, while in the New Zealand specimens they are 

 irregular foreign bodies (figs. 74l>, 751). Ehlers lias re- 



