MOUTH PARTS OF THE NYMPH. 



V— MOUTH PARTS OF THE NYMPH 



May-fly nymphs are divided systematically into three sub-families : the . 

 Ephemerinae, Heptageninae, and Baetinae. The Ephemerinae (PL II, fig. 23) 

 are mud or gravel dwellers. The bodies of those that live in mud are elongate 

 and cylindrical in form, with feet adapted for scooping, and mandibular tusks 

 for lifting. The Heptageninae (PI. II, fig. 22) are found in running water, 

 generally clinging to the under surface of stones. The head, thorax, abdomen 

 and lege are strongly depressed. The head margins are flaring to deflect the 

 current. The more generalized of the Baetinae (PI. II, fig. 24) inhabit the still 

 waters of ponds and pools. Some of this group intermingle with the Heptageninae 

 in the swift waters; others associate with the Ephemerinae on the sediment- 

 covered bottom in mud and silt. 



The food of May-fly nymphs mainly consists of algae, diatoms, and the 

 dead tissues of higher plants. Members of the Heptageninae have mouth-parts 

 adapted for scraping algae and diatoms from the stones. Rhithrogena uses the 

 blade-like distal segment of the maxillary (PI. V, fig. 60, Mx Pip) and labial 

 palp as a rake. The labrum in front, maxillae at the sides, and labium in the 

 rear brush the food into the mouth cavity. There it falls upon the molar surface 

 of the mandibles, and is ground. The Ephemerinae grind up the mud and silt 

 and digest the diatoms and plant waste. Among the Baetinae, some rasp and 

 strip pieces from roots and stones; some grind the silt in the manner of the 

 bottom-living Ephemerinae; and others have diverse brushes or bristles for use 

 in swift water. 



MUSCULATURE.* 



I. Labrum. 



Abductor (L'elevateur du labre, Str-D ; musculus levator labri, Bauer). 

 The abductors of the labrum (PI. II'I, fig. 3?, Abd.) are a pair of median muscles 

 originating in the front of the head between the antennae, and inserted in the 

 proximal portion of the labrum by a very short tendon. 



.Adductor. The adductors of the labrum (PI. Ill, fig. 35, ad) are two 

 two-headed muscles inserted by a long tendon, one at either side of the basal 

 angle. They are attached to the front of the head just below the bases of the 

 antennae. 



*0\ving to the various systems of nomenclature, uniformity in designating the muscles 

 of the mouth-parts is impossible at present. Since the musculature for May-flies is similar 

 to that reported for Gryllus by DuPorte (Ann. Ent. Soc. Am. 13:19-23), I have adopted his 

 system to avoid further confusion. Whenever possible, nomenclature previously used is 

 indicated. 



