RESUMEN
Mouthpart developmental histology of Whitmania pigra at different month of age were studied by paraffin section, HE staining combined alcian blue and periodic acid schifts reaction procedure (AB-PAS). The following results was obtained: Change ranges: oral width 0.6 mm (1-3 month), 1.2 mm (34 month); oral diameter 0.3 mm (1-3 month); 1.2 mm (34 month), the oral size reached maximum during 4-6 months and unchanged thereafter. Oral lip had a thin protective film located in the front of the mouthpart. The W. pigra possessed three jaws in oral cavity, the big one was in dorsum, the other two separated on both side of abdomen respectively. Jaws and muscular pharynx were interrelated closely. The jaws were composed by cuticle, epithelial layer, muscularis and jaw cavity from outside to inside. In the front of jaws had mastoid abdomen with function of secreting acidophilic granule from 2 month age. Oral cavity was composed by mucosa, submucosa and muscularis inside and outside. Oral cavity was rich of peristomial nerves. And pharynx was composed of mucosa, muscularis, adventitia from inside to outside. The folds height and width become heighten and thicken. Mucosa epithelium from complex flat epithelium changed into columnar epithelium, muscularis gradually developed into thickened along with growing. Muscular thickness reached maximum at 4 months. Mucous cells of W. pigra were classified into I-IV types based on different staining and two mainly morphological shapes (Tubular, Pear-shaped). Jaws, oral cavity, pharynx by AB-PAS staining showed little changes at different month of age. Mucous cells were few at 1 month age, and type II cells were increased rapidly in 2-3 month age in oral lip. Oral cavity contains more mucous gland cells type I. Under the muscularis there were connective tissues which distributed a few of mucous cells type II.