30 CTENOPHORES OF THE ATLANTIC COAST OF NORTH AMERICA 
Afterwards the deep, lateral furrows extend upward to the level of the 
apical sense-organ and the animal acquires the characters of Mnemiopsis. 
Thus the larve pass successively through stages characteristic of Pleuro- 
brachia, then of Bolinopsis, and finally Mnemiopsis. 
This species is common throughout the summer off the southern. 
coast of New England and is also found as far south as the Carolinas. 
It appears not to occur north of Cape Cod, Massachusetts. 
According to Hunter, 1904, Mnemiopsis leidyi rests at the surface 
with its mouth upward, and at the bottom of the aquarium with mouth 
downward. A constant electrical current of from 0.5 to 3 volts causes 
it to turn the aboral pole toward the anode and to move toward the 
cathode. It is relatively more resistant to decrease than to increase in 
temperature of the water. Responses to electrical stimulation under 
conditions of greater heat than normal show decrease in reaction time 
up to about 29° C., then rapid increase in reaction time. A slow increase 
in reaction time occurs below 15° C. 
Parker, 1905, finds that in Mnemiopsis and Pleurobrachia the combs 
beat metachronally, beginning at the aboral ends of the rows. 
In Mnemiopsis the 2 rows of plates belonging to the same quadrant 
beat in unison. This is often true in Pleurobrachia, although in this 
form all 8 rows may beat independently. 
The propagation wave shows scarcely any evidence of reversal in 
Muemiopsis, but often reverses in Pleurobrachia. Reversal of the effec- 
tive stroke of the plates was never observed in Mnemiopsis or Pleuro- 
brachia. 
A transverse cut across a row of combs in Mnemiopsis isolates the 
oral part of the row, which, however, soon recovers, although it beats 
independently of other rows. An isolated plate will beat if it retain a 
small amount of basal protoplasm. 
Cooling part of a row to 5° C. brings the movements of the cooled 
plates to a standstill, but does not interrupt transmission of the impulse 
to beat. Stretching of a part of a row also prevents movement, but 
does not prevent transmission. The transmission impulse is, therefore, 
mainly if not wholly nervous in nature, although probably supplemented 
by mechanical transmission from one comb to its neighbor. 
R. S. Lillie, 1908, finds that in Mnemiopsis mechanical stimulation 
arrests the automatic activity of the swimming plates. This, however, 
does not occur if calcium be absent, and the effect decreases as the cal- 
cium is decreased. 
Chun, 1880, finds that the litholite concretions of the sense-organs 
of Ctenophore are composed of calcium phosphate, whereas I find that in 
Scyphomeduse they consist of calcium oxalate. The functions of the 
concretions in respect to movement must therefore be quite different in 
the ctenophore and scyphomedusz. 
In this connection it is of interest to state that Samassa, 1892 
(Archiv far mikroskop. Anat., Bd. 40), finds that the litholites are not 
cell products, but are contained within epithelial cells which usually 
retain their nuclei, and are set free from the epithelium and gathered 
together in a mass at the apical pole. It will be recalled that Verworn, 
