228 ; The American Naturalist. [Mareh, 
I have given above my reasons for the separation of the 
_ Diplopods from the Chilopods, and need not repeat them here, 
I do not discuss the relations of the Diplopoda to the other 
_ sub-phyla, nor the relative position to be accorded the group. 
The ventral position of the gonads is a mark of low rank, but — 
in other respects the organization is much higher. 
ARTHROPODA OF UNCERTAIN POSITION. 
I—PYCNOGONIDA sIVE PANTOPODA. ‘ 
Regarding the systematic position of these forms I cannot 
add anything to the remarks of Morgan (’90), who has shown 
that not only in adult structure but in certain features of 
development, notably in the formation of the entoderm by 
delamination, they present conditions not easily paralled out- 
side of the Arachnida, and it is not impossible that they may 
belong there. The appendages are easily homologised in the 
two groups, and especially interesting is the fact that while 
most genera in the female retain a primitive condition 1n 
having the genital ducts open upon several pairs of append- 
ages (IV-VII), in a few these openings occur only on the 
seventh appendage, exactly where they occur in the Scorpions. 
II—LINGUATULINA.”" 
These forms, frequently associated with the Arachnids, pos 
sess but few points of similarity with them. Chief among 
these are the concentration of the nervous centres to a circum- 
œsophageal ring, and the peculiar arrangement of the ovaria? 
follicles. On the other hand, neither embryos nor adult resem- 
ble any Arachnids in more than a few superficial feature 
The opening of the genital ducts in the female near wae 
terior end of the body is not Arachnid in character, nor 18 © f 
absence of “liver” lobes from the mid-gut. Besides, a pa 
‘Arthropodan characters, may be mentioned the extensiv? 
celom and the outer circular body muscles. The spee A 
Pentastomæ have been so modified by parasitism that 1 
1! Upon points of structure and development consult Stiles (’91) and Spa en 
in addition to the older literature, 
ies of = 
