288 
CARNEGIE INSTITUTION OF WASHINGTON 
22) widely different hosts, including some from 168 fathoms as well 
as from shallow-water fishes. A massive infection in a ray ( Ptero - 
platea maclura) from 60 fathoms shows that very heavy infections may 
occur in nature. There are probably at least two other species at Tortugas 
related to Distomum fenestratum but with much smaller ventral suckers. 
The Cercaria L of Miller 1925 (Carnegie Inst. Wash. Year Book No. 24, 
p. 238) from Crepidula aculeata seems to resemble this species of trematode 
very much since the large vesicles or swollen regions of the cceca are char¬ 
acteristic. It is possible that the sexually mature adults are to be looked 
for among the Didymozoonidse. 
The life cycle of Helicometrina nimia (Linton) was discovered in part. 
The metacercarise are very commonly encysted in the thoracic region of 
Lysmata intermedia (Kingsley), a shrimp common among the Porites 
coral. The larvse also occur, although less commonly, in the snapping 
shrimp, Crangon formosum. The adult trematode occurs in at least thir¬ 
teen species of fishes. The fully developed metacercaria is recognized by 
the nine testes. The only other known Helicometrina (a new species) 
constantly has but five testes. Immature forms of H. nimia from fishes 
are indistinguishable from the metacercarise from the shrimps. The cer¬ 
caria of H. nimia is very possibly Cercaria J of Miller 1925 (Carnegie Inst. 
Wash. Year Book No. 24, p. 237) from Columbella mercatoria. At least, 
these cercarise readily encyst in Lysmata intermedia . An overdose of the 
cercarise proved fatal to four shrimps within a few hours. The cercarise 
agree in all respects with H. nimia except in position of the pharynx. 
Another partial life history became fairly apparent with the discovery 
that a Lepocreadid metacercarian very common as a free inhabitant (un¬ 
encysted) in the intestine of many fishes of depths from 40 to 60 fathoms 
agreed in every respect with a species of Lepidapedon found in the intes¬ 
tine of Epinephelas niveatus. The very general occurrence, the sharply 
limited depth distribution, and the fact that the metacercarian is an unen¬ 
cysted, juvenile form make this life history of especial interest. 
From the loggerhead turtle were secured several new records of trema- 
todes of that host in America. These include the Aspidogastrid, Lophotaspis 
vallei. Eggs of this trematode were found to hatch readily. The mira- 
cidium is elongate-oval in shape, varying, according to contraction, from 
150 to 210 p in length. There is a large sucker at the posterior end. Two 
eye-spots, close together, occur dorsally about one-third from the anterior 
end. The long cilia are limited to three ciliated plates, one at the extreme 
posterior tip behind the posterior sucker, the other two lateral just behind 
mid-body. The plates appear as transparent low elevations, 20 p in length. 
There is an elongate oral sucker at the anterior end, and an oval pharynx 
near the level of the eye-spots. No flame cells could be seen. The mira- 
cidium swims rapidly by means of its cilia, or it can creep into an inch- 
worm, extending its anterior end, releasing its posterior sucker, then 
pulling the posterior end up near the mouth. Five different cases of 
abnormal hatchings were watched in which the miracidium was reversed 
in the egg shell so that the posterior sucker emerged first. Such hatchings 
were difficult and often abortive or incomplete. 
Crustacea of the Tortugas Region , by Waldo L. Schmitt 
The general survey of the crustacean fauna which has been carried on 
during the past several seasons, has just about been brought to a con¬ 
clusion with the investigations conducted this year. The additional and 
TORTUGAS LABORATORY 
289 
improved equipment provided on the Anton Dohrn rendered it possible 
to carry vertical observations down to nearly 600 fathoms—a depth far 
exceeding any haul yet attempted by the laboratory and a record for 
the Dohrn. 
Of more than a dozen successful hauls this season from 100 fathoms or 
more, not less than six were made at depths between 290 and 580 fathoms. 
These have furnished extensive data bearing on a zone or zones not hitherto 
examined by us. It would seem that the bathymetric zonation of the 
deeper-water Crustacea, foreshadowed last year, may be even more sig¬ 
nificantly indicated when the studies upon the materials secured will have 
been completed. 
Noteworthy among the rarer forms obtained were several specimens of 
the Calappid crab, Acanthocarpus bispinosus , first described in 1880 by 
A. Milne Edwards from a single specimen taken by the Blake off the 
Grenadines in 140 fathoms, and so far as I am aware not again seen 
m the intervening half century. The Tortugas specimens are from 135 
to 168 fathoms, south of Loggerhead Key. It may here be noted that this 
species and the only other known member of the genus, A. alexandri 
Stimpson, which has been so abundantly represented in the Dohrn dredgings 
between 60 and 110 fathoms, are both stridulating crabs. This fact seems 
to have passed unnoticed, though the vertical flattened file of finely cut, 
close set, oblique ridges on the inner face of the palm and the suborbital 
row of sloping, a dash”-like tubercles on the carapace against which they 
play aie quite prominent structural features in these species. When touched 
or taken in the fingers under water, the crab may set up such a strong 
vibratory grating that the fingers are literally made to tingle. 
Considerable new information regarding the food of Tortugas fishes was 
derived from the stomach contents of a number of species not examined 
m past years. Of particular interest among the crustacean records so estab¬ 
lished was the discovery of a small Pandalid shrimp in the stomach of a 
flounder, Trichopsetta ventralis Goode and Bean, from 70 fathoms. Though 
differing markedly in rostral armature, it is very close to Parapandalus 
longicauda (Rathbun), which has only been found in 88 fathoms in the 
upper Gulf of Mexico and off Porto Rico in 200 to 225 fathoms. 
An additional specimen of Pasiphcea merriami described in last year’s 
report and another large individual of the giant isopod, Bathynomus 
giganteus, a male approximately 13 inches in length, were secured this year. 
The fair measure of success attending last year’s attempts to record 
visually the life habits of some of the Tortugas reef dwellers encouraged 
a little more intensive work in this direction during the last days of the 
period I was enabled to spend in study at the laboratory. Results, so 
far as the development of the film has progressed, are much better than 
were those obtained the preceding season. Further studies were made of 
the burrowing jaw-fish, Gnathypops, constructing its home and showing 
resentment at the too near approach of other fish to the entrance of its 
retreat. In alj, some 3200 feet of film were exposed. 
Effects of Radium Radiations on Regeneration in Euratella chamberlin, 
by Raymond G. Stone 
My studies on radiation and regeneration were continued from last 
summei. A more detailed investigation of the effects of combined beta 
and gamma radiations in comparison with those of the gamma rays alone 
