256 
PACIFIC SCIENCE, Vol. XI, July, 1957 
Wilson and Shimada (1955), and Wooster 
and Jennings (1955) discuss various aspects 
of the hydrography and biology of the eastern 
tropical Pacific. 
Several collections of zooplankton have 
been made in the vicinity of Peru — among 
them the Albatross, Dana, Discovery, and 
Carnegie collections— but analyses of the 
chaetognaths from these have not been pub- 
lished. During the course of a United States 
fisheries mission to Peru in 1941, Mr. Milton 
J. Lobell collected 25 plankton samples be- 
tween Callao and the Gulf of Guayquil in the 
period May 6 to 9 (Fig. 1). These samples 
form the basis of this report. 
Recently zooplankton collections have been 
made off Peru by Scripps Institution in 1952 
and 1955, and by the California Division of 
Fish and Game and the Bingham Oceano- 
graphic Laboratories in 1953 (Posner, 1954). 
The results of the plankton investigations of 
these institutions are not yet published, but 
the chaetognaths from the collections of the 
Scripps Shellback Expedition in 1952 (240 
samples), and of the California Department 
of Fish and Game Longline Expedition in 
Fig. 1 . Location of 1941 plankton samples. Every 
other station shown. Sample from station 9 not in- 
cluded in this report. 
1953 (26 samples), have been examined by 
the author. Part of the extensive 1952 ma- 
terial, in preparation for publication, is com- 
pared with the 1941 collection. 
METHODS 
The 1941 samples, preserved in dilute for- 
malin, were collected with a one-half meter 
net made of bobbinet. The exact mesh of the 
bobbinet is not known, but judging from the 
size of the specimens caught it appears that 
the mesh was within the range of one-half to 
three-quarters of a millimeter. All of the tows 
were made at the surface and were of five 
minutes duration. Because of the uncertainty 
of the mesh size and the unknown speed of 
towing, no attempt has been made to estimate 
the volume of water filtered by the net. In- 
stead the total number of specimens of each 
species collected in the tow is reported. 
The author has found the following papers 
helpful in identifying the chaetognath spe- 
cies: Michael (1911), Ritter-Zahony (1911), 
Tokioka (1939 and 1940), Daken and Colefax 
(1940), Thomson (1947), and Fraser (1952). 
The nomenclature of Furnestin (1953), has 
been used for part of the S. serratodentata 
group. 
RESULTS 
Fifteen species of Chaetognatha were found 
in the surface waters off the Peruvian coast in 
1941. Eight, or more than one-half of these, 
indicate warmer water present in May 1941 
than in August 1952. Of the eight species, 
five, Sagitta bedoti , Sagitta californica , Sagitta 
ferox, Sagitta neglecta, and Sagitta tenuis , in- 
vaded the Peru coastal waters from the north. 
Three species, Krohnitta pacifica , Sagitta regu- 
lars, and Sagitta robusta penetrated the coastal 
waters from the west or the north. The remain- 
ing seven species, Pterosagitta draco, Sagitta 
enflata, Sagitta hexaptera, Sagitta lyra, Sagitta 
minima, Sagitta pacifica, and Sagitta sp., prob- 
ably would show marked differences between 
May 1941 and August 1952 if it were possible 
