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; en, 

 entoderm;/, mesenterial filament; m, muscles; r, directive septa. 



D 



rn 



.. 



' 



FIG. 92 Cross- section of a fish passing through the fore limbs. DV, sagittal axis; 

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

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

 arch; lib, haemal 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). 



