426 Dr. H. J. Hansen on the Morphology of the 
with this the plate situated upon the outer side of this same 
first segment in Branchipus and Cladocera (§9), which 
probably subserves the purpose of respiration. In the same 
manner we may also explain the presence of the branchiz 
arising from the body at the base of the limb in Lophoguster, 
Gnathophausia, and Eucopia. 
25. According to $§ 22 and 18 the exopodite of the maxil- 
lule. and maxillee, if it is present at all, always proceeds from 
the third segment in the case of the orders mentioned ; it 
therefore follows that in these two pairs of oral appendages 
the primitive number of segments in the stem of the appen- 
dages is preserved and that the first segment comes to belong 
to the same category as the mandible, but not the coxopodite 
of the limbs. 
26. The Leptostraca are decidedly the lowest of the Mala- 
costraca. ‘he Myside stand much nearer to them than do 
the Kuphauside in the structure of the second pair of 
antennee (§§ 18 and 22), in the structure of the limbs, in the 
development of the larvee, in the presence of the furcal rami 
in the earlier larval stages (§18), in the shape of the heart, 
and in the presence of a conical projection for the orifice of 
each vas deferens ; they appear to me to be the lowest of the 
Humalacostraca. 
27. The old division into Thoracostraca and Arthrostraca 
strikes me as being quite untenable even when (with Grobben) 
we have excluded the Stomatopoda as being a section of equal 
value. ‘The arrangement appears to me to be based alto- 
gether too much upon only two conditions—the presence of a 
shield and of stalked eyes, as opposed to absence of a shield 
and sessile eyes,—and, moreover, none of these characters is 
constant (Tanaide, Cumacea). I consider that the Kumala- 
costraca can be arranged much better in three divisions, of 
which the first will contain the Mysida, Cumacea, Isopoda, 
and Amphipoda, while the second comprises the Kuphau- 
siida and Decapoda. The first division possesses a lacinia 
mobilis upon the mandibles ; eight segments in the limbs, of 
which the last segment ts cheliform and the first several times 
shorier than the second, while there are five segments before the 
knee ; a marsupium ; larve which are at first motionless and 
have a peculiar development ; an elongated heart ; shorter or 
longer processes for the orifices of the vasa deferentia ; and no 
spermatophores: while the second division is distinguished by 
having mandibles without a lacinia mobilis ; limbs composed 
of seven segments, of which the first ts almost as well developed 
as the second, while before the knee there are only four seg- 
ments, of which the fourth ts certainly homologous with the 
