DESCRIPTIONS OF GENERA AND SPECIES 519 



The buccal cavity is followed by an oesophagus which passes into the intestine at 

 about the eighteenth segment, but the exact position varies. 



The oesophagus is differentiated into a gizzard in most Acanthodrilidae ; in all 

 the members of the genus Benhamia and in Diplocardia there are, indeed, two 

 separate gizzards ; and in Trigaster there are no less than three of these organs. In 

 a few species, particularly those which are aquatic in habit, the gizzard is absent ; in 

 some of these species, however, the gizzard, although it appears on a superficial 

 inspection to be completely unrepresented, can, be recognized in longitudinal sections ; 

 it is so, for instance, with A. falclandicus (described by myself as A. georgianus). 

 The gizzard in all the Acanthodrilidae lies well forward, even so anteriorly as the fifth 

 segment (e. g. Octochaetus huttoni) ; it may or may not be confined to a single segment. 



Calciferous glands are very common, but not universal, in the family. They are 

 particularly prone to be absent in the genus Accmthodrilus itself; thus they are 

 said to be absent in A. pictus; in the genus BenhaTnia, on the other hand, they 

 appear to be invariably present, and to the number of three pairs; in Benhamia, 

 moreover, the calciferous glands seem to be more independent of the oesophagus 

 than is the case with other Acanthodrilids ; this, however, is not much more than 

 an appearance; for in A. dissimilis, for example, transverse sections show that the 

 calciferous glands are really quite distinct from the oesophagus, but, on account of 

 their large size, they completely encircle the gut, and, on dissection, seem to be 

 merely local thickenings of the oesophagus. The calciferous glands lie rather far 

 back as compared with many other earthworms, such as Pontoscolex; in Benhamia 

 they occupy segments xiv, xv, xvi, very often, if not always ; in 0. m^vltiporus the 

 last pair is even in segment xvii or xviii. For the details of the numbers of pairs, 

 and their position, in the different species, reference must be made to the descriptions 

 of the species. There is nothing characteristic about the structure of these organs 

 in the present family. 



The intestine begins as early as the sixteenth segment in Plagiochaeta, but usually it 

 does not commence before the eighteenth segment. In Plagiochaeta there is, according to 

 Benham, no typhlosole; in other species the typhlosole is variable in its development; 

 in 0. multipoTus the typhlosole is large and trifid in transverse section ; in A. novae- 

 zelandiae the typhlosole is inconspicuous ; in Benhamia there is a subsidiary typhlosole, 

 one on either side of the main typhlosole. Plagiochaeta is almost unique among the Oligo- 

 chaeta for the fact that the intestine is spirally twisted. The intestine is totally without 

 caeca or glands of any description. 



The nephridia in this family are sometimes paired and sometimes diffuse; in 

 the restricted genus Benhamia they are always diffuse ; so too in Octochaetus ; 



