-~ 
1886.] Zoblogy. 1061 
nida and Insecta, enabling their possessors to climb as well 
as walk. Podostomata have no urinary tubes. Limulus 
undergoes a slight metamorphosis, while in trilobites the adult 
differs from the larva in having a greater number of thoracic 
segments. 
m the Crustacea the Podostomata differ in the lack of 
functional antennz, and mouth-parts; in the compound eyes hav- 
ing no rods or cones, in the brain innervating the eyes (compound 
and simple) alone; in the shape of the head and pygidium or 
abdominal shield, and in the arterial coat enveloping the central 
nervous cord. 
The Podostomata are divided into two orders: 
Xiphosura, 
I. Merostomata, with three suborders : p ARE 
urypterida. 
II. Trilobita. 
—A. S. Packard, 
Oyster CULTURE.—Dr. J. A. Ryder has a paper on this subject 
in the Report of the U. S. Fish Commission, detailing the con- 
struction of apparatus for the artificial culture of oysters which, 
from a theoretical standpoint, certainly seems practical. His 
plans have been outlined in this magazine, and hence need not 
be repeated. One of the points brought out is that Lankester’s 
beautifully illustrated paper on green oysters (Quart. J. M.S. 
XXVI, pp. 71-94, pl. vIr, 1885) contains hardly an addition to our 
knowledge of this phenomenon, besides the conferring of the 
name marennin on the coloring matter absorbed. Almost every 
point made was previously published by Puységur, Descaine or 
Ryder from two to five years before. 
ECHINODERM DEVELOPMENT.—Fewkes has some observations 
on the development of Ophiopholis and Echinarachnius. He 
shows that in the former genus the endoderm arises by an invag- 
ination, but he cannot state the relations the blastopore bears 
to either mouth or anus of the pluteus. The mesoderm arises 
symmetrically either side the blastopore and apparently is of the 
nature of mesenchym, though not so stated. Nothing is given 
concerning the development of the mesothelial tissues. Aposto- 
lides who has previously studied the development of Ophiurans 
comes in for soñe apparently merited criticisms. In the sand- 
dollar, Echinarachnius, the early development is much the same. 
The pluteus is compared with that of Strongylocentrotus, from 
which it differs in the presence of large pigmen t-spots on each 
arm and the absence of “ ciliated epaulettes.” The whole of the 
pluteus is absorbed in the young sand-dollar, which has a very 
different appearance from the adult. = e development presents 
bar slight differences from other echinod 
