MOUTH PARTS OF THE NYMPH. 



In Ecdyurus, one of the Heptageninae, the hypopharynx (PI. Ill, fig. 37) 

 is not heavily chitinized and is relatively large. The compressors form a delicate 

 horizontal sheath (co) around the median lobe (m), and the depressors a vertical 

 sheath (d). The lateral lobe (1) is provided with one depressor (d) and two 

 compressors (co). 



In Callibaetis (PL V, tig. 67) and Baetis (PI. I. fig. 13) (Baetinae) no 

 musculature is evident within the hypopharynx. 



[V. Maxilla. 



Flexor. (Musculus flexor anterior, Bauer). The flexor of the maxilla 

 (PI. Ill, fig. 38, Fl) is a two-parted muscle attached to the outer edge of the 

 stipes (St) and inserted at the lower part of the central plate of the tentorium. 



Adductor. (Adducteur de la machoire, Str.-D. ; flexor maxillae, Burm. ; 

 musculus flexor maxillae Posterior, Bauer). The adductor of the maxilla (PI. 

 Ill, fig. 34, ad) is a two-parted muscle inserted at the outer and basal angles of 

 the cardo (Cd). It is attached to the lower surface of the central plate of the 

 tentorium. 



Abductor. (.Musculus flexor superior, Bauer). The abductor of the 

 maxilla (PI. Ill, fig. 38, Abd ) is a slender two-parted muscle inserted at the 

 lower inner angle of the galea-lacinia (Ga Lc) and attached to the posterior arm 

 of the tentorium. 



Flexor of galea-lacinia. The flexor of the galea-lacinia (PI. II'I, fig. 38, Fl) 

 is inserted at the outer angle of the stipes (St) and attached to the galea-lacinial 

 .- pi dome ( ap ). 



Maxillary Pali'. 



Extensor. (Musculus extensor palpi maxillaris, Bauer). The extensor of 

 the maxillary palp (PI. Ill, fig. 38, e) originates at the stipital apodeme and is 

 inserted at the outer angle of the base of the first palp segment. 



Flexor. The flexor of the maxillary palp (PI. Ill, fig. 38, f) originates at 

 the stipital apodeme and is inserted at the inner angle of the base of the first 

 palp segment. 



The flexor (Musculus flexor articuli palpi maxillaris, Bauer) of the second 

 palp segment (PI. Ill, fig. 38, f) originates at the outer basal angle of the first 

 segment, and is inserted by means of a slender tendon into the inner basal angle 

 of the second segment. The extensor of the second palp segment (PI. Ill, fig. 

 38, e) originates at the inner basal angle of the first segment and is inserted into 

 the outer basal angle of the second segment. This system of cross attachments 

 gives greater leverage to the blade-like distal segment. In those forms where 



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