PACKARD.] MORPHOLOGY OF PHYLLOPODA. - ol 
XIV, fig.4). The body-walls are rather thick and the muscles are well de- 
veloped, particularly the dorsal extensor muscles, and the motor or exten- 
sor muscles of the limbs, which Hee 
arise in part from the dorsal re- os 
gion, and in part from the sides 
and sternal region. The body 
cavityisrathersmall. Theheart J /------(----. 
is large, either cylindrical as in 
Estheria, or fattened asin Tham- 
nocephalus. The digestive tract 
is large, capacious, and the cav- 
ity of the head is mainly filled 
with the two liver masses; the 
brain being remarkably small, 
while the nervous cord, especially 
the brain and succeeding gan- 
glia, are remarkably small and 
weak, compared with other Crus- 
tacea, either the malacostracous 
or the entomostracous orders ; 
this peculiarity is well brought Fic. 25.—Section of Apus. ht, heart; int, intestine; 
out in the transverse sections, fife fnathovase! gill and 7b, labellum, represeating tho 
thoracic ganglia, particularly in Hstheria (Plate XXIV, figs. 9 n, 9), is 
noteworthy. The apparent bulk of the body is largely due to the large 
size and nature of the leaf like or foliaceous appendages, with their 
broad attachments ; the latter peculiarity is characteristic of the Branch- 
iopods in general and the Phyllopods especially, and is quite different 
from the definite, small coxal articulations of the legs of Malacostraca 
or Copepoda. The ovaries or testes, according to the sex, form a large 
lobulated mass extending along each side of the digestive canal, as far 
forward as the base of the head. Their relations in Apus are seen in 
Plate XXXII, fig. 2, and in Thamnocephalus in Plate XIV, fig. 4. 
Nomenclature of the body-regions and appendages.—As the terms “ head,” 
“thorax,” and “abdomen” are more or less inexact when used for Arthro- 
poda as compared with the worms and molluscs, as well as vertebrates, 
there should be suitable designations for these regions. 
In 1869, in our Guide to the Study of Insects, we proposed the term 
arthromere for the segment or ring forming the primary element in the 
composition of the body of any jointed or articulated animal. The 
terms “zodnule,” ‘ zodnite,” “ zonite,” and “ somite,” have been used by 
various authors, but these terms have been used rather indiscriminately, 
and we therefore suggested the term arthromere tor the body segments 
of articulated animals (worms and arthropoda). While the term ‘‘somite” 
or ‘‘zonite” may be properly applied to the rings of worms and other ani- 
mals as the Chitous, we would suggest that the term arthromere be re- 
stricted to the segments, or body-elements of Arthropoda, 
For the three primary regions of the head the only scientific terms as 
yet in use are those proposed by Prof. J.O. Westwood in Bate and 
Westwood’s History of British Sessile-eyed Crustacea (vol. 1, p. 3). 
These are cephalon tor the head, pereion for the thorax, and pleon for the 
abdomen; while the thoracic feet are termed pereiopoda anu the abdom- 
inal legs pleopoda ; the three terminal pairs being called wropoda. 
As the names applied to the thorax and abdomen have no especial 
morphological significance, the Greek zepatov, simply meaning ulterior, 
and zicuy, more, we would suggest that the head of Arthropoda be termed 
the Cephalosome, the cephalic segments cephalomeres, and the cephali¢ 
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