190 BULLETIN OF THE BUREAU OF FISHERIES. 
Nympx-Sk1n Counts, Ponps 1 To 4 D, Fatrprort, Iowa, 1916. 
Nymph skins obtained. July 3. July 16. July 31. Aug. 15. 
, No. | P.ct.| No. | P.ct.| No. | P.ct.| No. | P.ct. 
Aeschiia Gonbtricts $5 04. 7.5: SLE. SUSE AV a, Teh toe oh pod er ail bak 30] 5 20 4 
PATS So OE ee Cee een SEES ee Hane eO nO cSUN Eerie an snc sorene CH eRe 10 2 46) 7 48] 10 
Epicordubapricepst.). 266.5... 0k. Ae. NES SB. DONG. aes. F 31 6 ir veer... 12| 2 Is 3 
Panitalahiavescensy ssi cc) Sis spiel okt aietwhre baile s.avigia\e mpeia/osuk n’ope civ sisicia wall wig Gereseicie| se cle | Uibiclte el Seaeesl sfalia A aoe + ro 2 
Tramealacerata ...60.0..6. eee el la. celemithe Se REDE RP res ECE ae Britt SS Bie LEe a altiriods 40 8.5 
Perithemisdomitia............. eh Gaga BE lated ry Bees 
Celithemiseponina............. 5 3\ aaa de- 16| 2.5 8 2 
Leucorrhiniaintacta........... 2 ve \Gogene | nei 25 5 
Sympetram rabictindtdliami pF SLT RSS RLU SATS REL PEA oe Io 2 1z2| 2 26 5-5 
Sympetrum corruptum.. . A RY Eee ra APES con Sel adanee psee sel eactas. 
Pachydiplax longipenni: ae THER. OJ 6 I sr| 8 20 4 
Libellulaluctuosa........ 20... sue. es eee Bp en ras 442 89 | 310 66} 246 | 4o 137] 29-5 
Bibellifia pullchiella nid $6.6 EOE QA ot aeRO TE tS RSET ruts eh 6 I 20] 3 a RIESE 
Erythemissimplicicollis... 2.0 ....0.0 00.00 e sec eee ae EEN chee Bae 3 or eee 114 24 | 160 | 26 112] 24 
Plathemislydia.................4.. TiRGARe POT, SASATEL ERR LT RA 5 a EICER GL SR Bi rsh ALOR |S 
Certain additional facts were noted during the gathering of the nymph skins. 
1. CHOICE OF LocaLity.—Upon reaching maturity the nymph does not crawl out 
of the water blindly wherever he may happen to be, but shows a definite preference for 
certain localities. Most of the nymphs here recorded transform in the early morning, at 
which time the west and north margins of the ponds receive the early sunshine, while 
the east and south margins are in the shade. It has been stated that the counts were 
made on the north shores; this was because those shores were found by actual trial to 
yield many more nymph skins than the east or south shores, and considerably more 
than the west shore. Another important reason is that the north shores border the | 
shallower water of the ponds, and are thus naturally frequented by the nymphs when 
nearly ready for transformation. 
A third factor which may influence the nymph in its choice of a locality for transfor- 
mation is the kind of support obtainable. Some nymphs, such as those of Libellula 
luctuosa, Anax, and Epicordulia crawl up on anything that may be convenient, including 
wire screening, old boards, fence posts,and the like. Others show a decided preference 
for certain kinds of support and will even choose between different water plants. 
Erythemis simplicicollis, for example, selects the arrowleaf, Sagittaria latifolia, in 
preference to the cat-tail, Trypha latifolia, when the two are equally available. And 
this same species was the only one found in any abundance upon the stems of the crex 
grass, Carex stricta. 
Erythemis transforms later in the day than many of the other species, and its 
exuviz were found in large numbers along the eastern shores of the ponds. In five of 
the ponds these shores contain both cat-tails and arrowleaf in addition to the crex grass, 
but almost without exception the Erythemis nymphs had chosen the latter. 
On the other hand, Anax usually emerges during the night, and its exuvie were 
found upon the western and northern shores, and more of them upon the cat-tails than 
upon all other kinds of support combined. The large, sprawling nymphs of Tramea 
lacerata also take very kindly to the cat-tails, but shun the crex grass altogether. 
Among the damselflies the Enallagmas are always found upon some convenient stem, 
a short distance above the water. Often there will be several exuvize upon the same 
stem, and in one instance the number reached 21, as recorded upon page 230. 
On the other hand, the nymphs of Ischnura very frequently crawl out upon the 
top of the lily pads and perch for transformation on the margin of the leaf, where it has 
