1884. | Ze ool ogy. 431 
Spencer’s I-10 inch immersion objectives, and as these appendages 
can be seen with ordinary objectives in very much smaller mites 
than this, it is safe to assume that there are none. The charac- 
ter of the legs, with their chitinous rings and highly-developed 
epimera, would seem to be sufficient to place this form with the 
Sarcoptidz, even if none of the other stages existed. The legs 
are not terminated by two hairs, as is supposed by some writers, 
but in the three anterior pairs by a long claw with a slightly 
swollen tip, which probably represents the tarsal sucker of the 
normal form.—H. Garman. 
On THE MORPHOLOGY oF THE “ LATERAL RODS” OF THE OPHIU- 
RoD PLureus.—Two groups of Echinoderms, the Ophiuroidea 
and the Echinoidea, have a larval stage in their development, 
which is known as a pluteus. In both of these groups the larval 
appendages, unlike those of the young of other Echinodermata, 
have the form of long calcareous rods, encased in a covering like 
that which forms the fleshy walls of the body. 
Homologues of all these appendages or rods of the Ophiuran 
Pluteus have been found in those of the Echinoid, with the excep- 
tion of by far the most prominent pair, which is first to appear 
_ and last to be absorbed and known at the lateral arms These 
are Not commonly mentioned as existing in the pluteus of the 
4 
‘ 
i 
i f 
4 inoid genera, and many authors say that they are unrepre- 
_ Stnted. On the other hand a pair of appendages, which seems to be 
_ Without homologues in the pluteus of the Ophiuran, exists in the 
| ee of certain genera of Echinoidea, as Arbacia, and are called 
© apical” or “anal” rods or appendages. The lateral rods of 
the Ophiuran larva bear so many resemblances to these so-called 
g the appendages of Arbacia, that it seems natural to homologize 
one pair with the other. 
“(sled pluteus from the Bermudas, a description of which I 
: rs angel to publish, seems to stand intermediate between that of 
and the young Ophiuran in respect to the size, and com- 
: veia ticulars the homology of these two appendages which I 
n b 
: a rel. 
sha Pluteus o Ophiurans takes place, and that when the apical 
which | bacia develop, may not seem to support the theory 
er eebe advanced in regard to their homology. The 
to develop, while the posterior pair of arms in Arbacia 
ag Oped, and the so-called antero-lateral are far along 
— Ore any trace of the apical rods appears. This 
oe development would seem a fatal objection to the pro- 
ip i 
P ve netlatre of the arms adopted here is that used by Balfour in his Com- 
ay SA ology, Volt, page 470. 
