32 CTENOPHORES OF THE ATLANTIC COAST OF NORTH AMERICA 
parent as in M. leidyi. The outer surface, instead of being smooth as 
in M. letdyi, is besprinkled by numerous small warts, which are, how- 
ever, not found between the subtentacular rows of combs, but are well 
developed on the sides of the oral lobes. The windings of the meridional 
ventral canals through the oral lobes are far more complex than in M, 
Jeidyi, and the canals are of a decided purple color. This is the most 
tigid ctenophore known. The animal may be removed from the water by 
hand without suffering injury. The mature ova are similar in form to 
those of M. leidyi. I first found this ctenophore in Charleston Harbor, 
South Carolina, late in summer, and again in considerable numbers off 
Port Townsend in Kingston Harbor, Jamaica, late in March, 1909, and 
in May, 1911. It is said by local fishermen to be common throughout 
the summer at Jamaica. It lives well in aquaria, and is doubtless the 
most favorable form among ctenophore for physiological experiments. 
It is greedily devoured by the scyphomedusa Dactylometra. When 53 
mm. long the young animal is of a glassy transparency, and has all the 
structural features of Mnemiopsis. 
The following table gives the dimensions in millimeters of two 
mature specimens of this ctenophore found off Port Henderson, Kings- 
ton Harbor, Jamaica: 
Mar. 22, 1909. May 1, torr. 
Total length of body .........ecceeeec ee aeeee 108 96 
Stomodeal diameter .........seeeeeeer eens 44 44 
Tentacular diameter .... 24 34 
Length of oral lobes........ 39 25 
Length of auricles........ceceseeeeeceeeveres 26 29 
Depth of cleft of sense-organ........-.sees0. 1s 15 
Length of subtentacular rows of combs..... 60 
This species is distinguished from M. leidyi by the extraordinary 
tigidity of its gelatinous substance, the complex windings of its merid- 
ional ventral canals in the oral lobes, its amber-greenish opalescent color, 
and the wart-like protuberances over the sides of the oral lobes. 
If this ctenophore be placed in 33 parts of sea-water + 67 parts of 
o.4 molecular magnesium chloride the cilia cease to beat for about 3 
minutes, after which waves begin to course with abnormal rapidity down 
the rows of combs, the movement being coordinated as in natural sea- 
water, but of far greater energy and speed; the stimuli following closely 
one upon the other so that several waves are commonly traveling down 
the same row of combs at one and the same instant. This abnormally 
rapid movement of the cilia continues more than 15 hours, the muscles 
during all this time being incapable of contraction. 
If, on the contrary, the ctenophore be placed in 33 sea-water + 67 
parts of 0.625 molecular sodium chloride the rows of combs cease to beat 
at the end of 12 minutes and the cilia along the auricles at the end of 
19 minutes, while the muscles are highly excited and contract spas- 
modically more than half an hour. The auricles lack muscles and are 
almost incapable of contracting. A local contraction of the muscles 
causes the cilia overlying them to cease beating until the muscles relax, 
