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ANATOMY AND HISTOLOGY OF PLEUROCH ATA MOSELEYI. 503 
anterior mesenteries described above is also found in Urocheta, though, 
whether a modification of this kind can be made use of for the determination 
of systematic relations is perhaps more than doubtful. The structure of 
the alimentary canal at once distinguishes Plewrocheta from any described 
genus, as does also the distribution of the sete. There seem to be no special 
relations with the Anteclitellians, except perhaps the absence of “ cceurs 
intestinaux.” 
This résumé of the structural relation of Plewrochwta with other forms, 
leaving out for the present the consideration of the generative apertures, shows 
that it occupies a position between the Intraclitellians and Postclitellians, with 
perhaps rather closer affinities to the latter group, but that it cannot definitely 
be classed with either, but ought rather to form a group apart. This conclusion 
is stengthened when we come to study the generative apertures; they are so 
peculiar that they cannot be considered as conforming to the Postclitellian or 
Intraclitellian type, though they are more closely allied to the latter than to the 
former. We must then either regard the existing classification of PERRIER as 
unsatisfactory, since it is not elastic enough to comprehend this new genus, or a 
new group must be formed and added to the three groups already created by 
PERRIER ; on the whole, the latter seems to be the wisest course. The state of our 
knowledge with respect to the Oligochwta, as has been remarked several times 
in the course of this memoir, is by no means advanced, and therefore it is use- 
less at present to alter a classification which is extremely convenient ; whether 
it will prove to be of permanent value is another question, which cannot yet. be 
answered. On the principle of nomenclature adopted by PeERrtER for the 
classification of the Oligochwta Terricola, it does not seem easy to select a name 
that will have any meaning ; perhaps Jn/raclitellian will do, though it must be 
admitted that the name is not a very expressive one. 
Returning to the description of the generative organs. Pleurocheeta pos- 
sesses one pair of testes situated in the 12th segment (see Plate XXV. fig. 7; 
Plate XXVII. fig. 10), and presenting the appearance of racemose glands, 
which is an extremely unusual character in the Oligochwta, but is paralleled in 
the case of Plutellus* and Digaster. 
In the 11th and 10th segments are two pairs of complicated folded organs 
(Plate X XVI. fig. 8), concerning the nature of which there is some uncertainty ; 
they lie in either case on the posterior wall of their respective segments, and 
they are each continuous with a fine duct which runs backwards perforating the 
mesentery, and is lost in the body wall of the segment behind ; it seems likely 
that these fimbriated organs are the expanded terminations of the vasa deferentia, 
but in this case we should expect to find them uniting into two tubes running 
down the body wall on either side of the nerve cord ; nothing of this sort was 
* Perrine, “ Etude sur un genre nouveau de Lombriciens,’ Arch. Zool. Exper., vol. ii. 1873. 
