And zooukogjraphy of ixdian oligoch^eta. 107 



definitely begin). The presence of septa between the successive 

 gizzards seems to be a necessity for their development as separate 

 structures, and two gizzards probably could not develop in the 

 majority of species of Octochcetus, where one, two, or three septa 

 are absent in the gizzard region ; an extension of the muscularity 

 of the oesophagus would simply result in an increase in the size 

 of the existing gizzard. In Trigaster, with two or three gizzards, 

 the septa are all present. I am not acquainted with the facts in 

 all the numerous species of Dichogaster, but the septa are certainly 

 often present ; in D. malayana, where there is no septum 5/6, 

 separate gizzards are, according to my observation (9), scarcely 

 discernible in segments v. and vi. — they seem to have " run 

 together," as it were. In the single species of the genus Mono- 

 gaster — essentially a Dichogaster in which there is only one 

 gizzard — the septa in the gizzard region are wanting (6) and the 

 two gizzards of the Dichogaster ancestor have doubtless " run 

 together." In those species of Dichogaster where septa are absent 

 in the region of the gizzards (e. g. D. crawi) Ave may perhaps 

 predict that the gizzards will not remain long separate, and that 

 the condition of Monogaster will be arrived at. We may conclude 

 that the -duplication of the gizzard, while impossible in the 

 majority of species of Octochcetus, would be possible in the primi- 

 tive group consisting of 0. bis7iambari,pachpaharensis, andpallidus, 

 and seems to be in process of accomplishment in 0. pallidas. 



Next with regard to the calciferous glands : in Eudichogaster 

 these organs are in segments x.-xii. or thereabouts, in Octochcetus, 

 usually, in segments xv. or xvi. It would, I think, be difficult to 

 derive Eudichogaster from Octochcetus if these were constant 

 characters of the two genera (though Michaelsen, deriving Dicho- 

 gaster from Eudichogaster (4), sees no difficulty, apparently, in 

 assuming a dislocation of the glands backwards ; in deriving 

 Eudichogaster from Octochcetus— from the usual type of Octochcetus 

 that is — the dislocation would have to be forwards). But the 

 more primitive species of the genus Octochcetus (0. bishambari, 

 pachjyaharensis, and j^Midus) have no calciferous glands ; in 

 Eudichogaster bengalensis, as has been seen, they are at a very 

 low level of development ; the morphological similarity, in this 

 respect, between these species of Octochcetus and Eudichogaster is 

 just as close as that between Trigaster and Eudichogaster, and the 

 derivation of the one from the other just as easy. 



It will be remembered that one reason for deriving Eudicho- 

 gaster from Trigaster rather than from Octochcetus was the 

 similarity of the nephridial condition in E. ashworthi and 

 T. lankesteri, and the dissimilarity between E. ashworthi and 

 0. thurstoni. But a wider survey of the nephridia of the latter 

 two genera shows that not all Eudichogasters are in the same 

 condition as E. ashworthi, and that not all species of Octochcetus 

 are like 0. thurstoni. Of the six species of Eudichogaster where 

 the descriptions are sufficiently detailed to be of use, in only one 

 other (E. prccshccdi) is the nephridial system capable of being 



