PACKARD.] 



MOKPHOLOGY OF PHYLLOPODA. 



371 



Fig. 25. — Section of j4pus. ht, heart; int, intestine: 

 ng, ganglion ; c, carapace; 1-G, the six cxites, 1 being 

 the gnatbobase ; gill and fb, ilabelium, lepreseuting the 



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 

 arise in part from the dorsal re- 

 gion, and in part from the sides 

 and sternal region. The body 

 cavity is rather small. The heart 

 is large, either cylindrical as in 

 Estheria, or flattened as in Tham- 

 iiocejylialus. 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, 

 whilethe 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 jieculiarity is well brought 

 out in the transverse sections, 

 where the diminutive size of the exltes 

 thoracic ganglia, particularly in Estlieria (Plate XXIY, figs. 9w, 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 gener.d and the Ph^llopods especially, and is quite different 

 from the definite, small coxal articulations of the legs of Malacostraca 

 or Cope])oda. 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 Thamnocephahts in Plate XIY, fig. 4. 



Nomenclature of the hody-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 i)roposed 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 "zoonule," "zoonite," "zonite," and " somite," have been used by 

 various authors, but these terms have been used rather indiscriminatelj', 

 and we therefore suggested the term arthromere for the body segments 

 of articulated animals (worms and arthroi)oda). While the term "somite" 

 or "zonite" may be properly sqjplied to i he rings of worms and other ani- 

 mals as tlie Chitons, 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 for the head, pereion for the thorax, and pleon for the 

 abdomen; while the thoracic feet are teYmed pereiopoda ami the abdom- 

 inal legs pJeo2)oda ; the three terminal pairs being called uropoda. 



As the names applied to the thorax and abdomen have no especial 

 morphological significance, the Greek Tispaco'^, simply meaning ulterior, 

 and -Xeov, more, we would suggest that the head of Arthropoda be termed 

 the Cephalosomej the cephalic segments ceplmlomeres, and the cephalic 



