NARRATIVE OF THE EXPEDITIONS 
The general account of the Irwin Expedition was published by Eigenmann 
(1919a, 1920a, and 1922b). My own part in the undertaking covers the areas 
which we have under consideration here, and may be extracted as follows (Allen, 
1920): 
_.. All members of the party reached Lima, Peru, in August, 1918. My chief 
activities were the collection of parasitic materials, and the collection of the 
fishes of the Titicaca basin... . As an introductory procedure I worked about 
Lake Junin in Central Peru and spent more than a month along the Huallaga 
from its sources near 14000 feet down to 2000 feet. 
After early September the writer proceeded independently of the others, 
first to Lake Junin and the Rio Huallaga, later to Lake Titicaca. Lake Junin 
(Chinchayeocha) is a shallow, mud-bottomed lake near Cerro de Pasco. It is 
surrounded by great areas of marsh and lies in the midst of an extensive peaty 
pampa at more than 13500 feet elevation. It forms the source of the Rio 
Mantaro, one of the principal tributaries of the Ucayali, and this in turn one 
of the three principal tributaries of the Amazon. The inhabitants regard 
it as the true source of the Amazon, an honor it shares with a score of high 
Andean rivers. 
The pampa is a bleak area upon which virtually nothing grows except certain 
native sessile rosette-plants, representing several families, but principally 
composites. These constitute the pasturage of the few sheep and llamas that 
can be maintained. Everywhere in the Peruvian Andes there is a remarkable 
climatic difference between elevations of 12000 and those of 13000 feet. Though 
Lake Titicaca is five hundred miles farther from the equator than Junin, there, 
at 12500 feet, an extensive agriculture is practised. Wheat, barley, and 
potatoes are rarely seen at elevations of 13000 feet, and the Junin pampa will 
produce none of them. At midday temperatures may be quite high. But 
nights are always cold, and the passing of a cloud over the face of the sun will 
cause the fisherman to assume his coat. At equal elevation at Cebollar, Chile, 
a diurnal temperature variation of 65°F. was encountered. 
While the elevation is too great to allow more than a few land plants, there 
is still an abundance of aquatic vegetation. The lake bottom is deeply covered 
with mud and floeculent organic debris. Ceratophyllum, Potamogeton, and 
Philotria are abundant. The exposed roots of the shore plants at the water’s 
edge are covered with great quantities of green fresh-water sponge, of which 
adequate collections were made. 
The fish are of only two species, but very numerous in individuals; they 
are: the bagre, a Pygidium, catfish, which the inhabitants say ascends the 
rivers to spawn; and the challhua, an Orestias. 
The fish are only slightly susceptible to dynamiting. It affected only those 
nearest the explosion. Most of these instead of rising to the surface as was 
expected sank into the ooze at the bottom and were lost. At first one is 
inclined to attribute this to the great elevation, and the decrease of about two- 
fifths of the atmospheric pressure. But the fishes here are apparently in as 
perfect adjustment to the existing hydrostatic pressure as at any other eleva- 
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