Systematics of certain Chilognathous Diplopods. 517 
Syst. xiii. pp. 53-54, 1900). In the Ascospermophora 
(Chordeumoidea) no seminal sacs have been developed 
within the appendages of the seventh segment, their function 
being performed (according to Verhoeff) by the exsertile 
coxal pouches of the two pairs of appendages of the eighth 
segment. Hence there are neither true phallopods nor 
coleopods. It is hard to believe that this condition has been 
derived from the advanced state seen in the other groups of 
Helminthomorpha, where genuine phallopods have been 
developed from the anterior or posterior pair of the seventh 
segment. In the Proterospermophora (Lysiopetaloidea, 
Polydesmoidea) phallopods resulted from the transformation 
of the anterior pair of the seventh segment, the posterior 
pair reverting to the primitive type of locomotor appendage. 
In the Opisthospermophora they arose from the posterior 
pair, the anterior pair taking on the function of coleopods, 
the condition characteristic of both groups being derivable 
from the hypothetical stage in which both pairs of the ap- 
pendages in question were modified simply as spermato- 
phore-holders. 
To the Opisthospermophora belong the Iuloidea, Spiro- 
streptoidea (sens. lat.), Spiroboloidea, and no doubt also the 
Stemmiuloidea. Setting aside the Spiroboloidea, these 
groups further resemble each other in possessing a distinct 
penis. In the primitive Diplopod there were probably two 
penes emerging behind the appendages of the second pair. 
They are retained as such in the Limacomorpha. In the 
Colohognatha they are also distinct, although united to the 
coxee of the appendages, being long in the Polyzonide, short 
in the Siphonophoride and Platydesmide, where they appear 
as papilliform excrescences of these segments. The fusion 
initiated in these families is carried to an extreme in the 
Chordeumoidea, Lysiopetaloidea, Polydesmoidea, and Onisco- 
morpha, where the penes have disappeared as independent 
structures, the seminal ducts perforating the coxe of the 
appendages in question. In the Juloidea and Spirostrep- 
toidea the two penes have fused together, though the organ 
still shows unmistakable traces of its double origin. In the 
Stemmiuloidea the fusion is much more complete, all indica- 
tions of the primitive double nature of the organ having 
disappeared, the process resulting in the formation of a long 
apparently bisegmented organ. The total suppression of 
the penis in the Spiroboloidea may be regarded as a specialized 
feature probably resulting from a gradual diminution in size 
of the small double penis such as is seen in the Spirostrep- 
toidea. Thus it is possible to trace back all the modifications 
Ann. & Mag. N. Hist. Ser. 7. Vol. xii. 34 
