32 CTENOPHORES OF THE ATLANTIC COAST OF NORTH AMERICA 



parent as in M. leidyi. The outer surface, instead of being smooth as 

 in M. leidyi, 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. 

 leidyi, and the canals are of a decided purple color. This is the most 

 rigid 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, 191 1. 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 ctenophoras 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: 



This species is distinguished from M. leidyi by the extraordinary 

 rigidity 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 -f 67 parts of 

 0.4 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 -f 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, 



