PROMORPHOLOGY 



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main and the sagittal axis is the sagittal or median plane and it divides the 

 animal into symmetrical halves. A frontal or horizontal plane passes through 

 the longitudinal and transverse axis, separating dorsal and ventral halves. 



Fig. 91. — Section of a young sea anemone (after Boveri). ss, sagittal plane; 

 tt, transverse axis; I, II, III, septa of first, second and third orders; ek, ectoderm; e«, 

 entoderm;/, mesenterial filament; «;, muscles: r, directive septa. 



Fig. 92 — Cross- section of a fish pas.sing tlirough the fore limbs. DT', sagittal axis; 

 RL, transverse axis; a, dorsal aorta; c, body cavity; d, gut; cli, notochord; g, shoulder- 

 girdle; h, heart; m, muscles; n, anterior end of the kidneys; p, pericardium; ob, neural 

 arch; itb, ha:mal arch; r, spinal cord. 



A transverse plane passes through transverse and sagittal axes, separating ante- 

 rior and posterior parts of the body. The great majority of animals belong here 

 (fig- 92). 



