1885.] The Inter-Relationships of Arthropods. 565 
This comparison brings the beginning of the abdomen in the 
same position in each group, but we have no other features to 
test its validity as we had in the case of the Acerata and Crusta- 
cea. In the hexapods there is nothing which in any way resem- 
bles a segmental organ. 
The hexapods have no liver, an organ voluminously developed 
in Acerata and Crustacea; their genital ducts terminate at the 
end of the body, and no evidence as yet presented points to the 
conclusion that they are to be regarded as modified segmental 
organs. 
With regard to the myriapods the problem is more difficult, 
and our knowledge of the development is too scanty to throw 
much light on the subject. The attempt has often been made to 
homologize the mouth parts in the two groups, but as yet with 
not very satisfactory results. A few morphological facts may 
prove suggestive. As is well known the myriapods are divided 
into two groups, Chilopoda and Chilognatha, represented by 
Scolopendra and Julus respectively. In the Chilopoda the geni- 
tal ducts terminate at the end of the body beneath the anus, in 
the chilognaths near the anterior end of the body, in a position 
almost comparable to that in the Acerata. In the chilopods the 
stigmata occupy the same position (between the dorsal and ven- 
tral plates) as in hexapods, but in the chilognaths they may 
occur on the ventral plates or even in the bases of the legs. Ap- 
parently in both groups the antennz are pre-oral in position; in 
the chilognaths their nerves arise in advance of those to the optic 
organs. 
In this connection more knowledge, especially of the head, is 
desirable concerning the curious fossil myriapod, Acanther- 
pestes, described by Mr. Scudder. Scolopéndrella will also repay 
investigation. In these forms, between the bases of the legs are 
the openings of peculiar organs. Mr. Ryder regarded those of 
Scolopendrella as tracheal stigmata ; Mr. Scudder those of Acan- 
therpestes as supports for branchiz. It may turn out, indeed it 
is probable, that both are the outlets of segmental organs. 
The few facts here presented, when taken together with the 
preceding remarks on trachez and Malpighian tubes, would allow 
the supposition that the myriapods may have but little relation- 
ship with either hexapods or spiders, and even that chilopods and 
chilognaths are not so closely connected as is usually supposed. 
VOL. XIX.—NO. VI. 37 
