[145] NOTES ON ENTOZOA OF MARINE FISHES. 863 



form. Circular os at apex of head from which sixteen soft tentacle- 

 like proboscides may be protruded. Neck none. First segment short ; 

 succeeding segments often moniliform, then lengthened ; last segments 

 four or five times as long as broad, loosely attached to each other. 

 Genital apertures marginal ; cirrus echinate, ova numerous with thin 

 membranous shell. Strobile small, so far as observed not exceeding 



gmm 



Habitat. — Trygon centrum, spiral valve, August 1, 3, and 10, 1887. 

 Wood's Holl, Massachusetts. 



During the month of July and August, 1887, I made careful and 

 painstaking search for entozoa in the sting ray (Trygon centrum). On 

 three different occasions, in the course of these examinations, I found 

 a few small cestods in the spiral valve which I at first took to be frag- 

 ments or immature forms of some of the various species of the Tetra- 

 bothriidce which I found at the same time in most of these hosts. On 

 one occasion, however, I examined a sting ray which yielded no entozoa 

 except these small forms, a very minute Rhynchobothrium and a few 

 cysts from the stomach wall. When these small cestods were exam- 

 ined, while they were yet alive, they showed no sigus of activity in the 

 sea-water in which they had been placed, and as the short chains of 

 segments all exhibited a tendency to fall to pieces readily, the idea 

 was naturally suggested that they were Tetrabothriidw which had been 

 introduced into the ray in a mature condition along with their proper 

 host and had succeeded in resisting the action of the digestive fluids 

 of the ray for a while, but were now succumbing to the influence of 

 their uncongenial surroundings. 



On account of the number of larger and more attractive new species 

 that were collected at the same time, these very small and apparently 

 unpromising forms were given but a superficial examination at first. I 

 found, however, that they possessed four bothria or acetabula and a ter- 

 minal opening at the apex of the head. It was only after the specimens 

 had lain for some time in alcohol and I had leisure to study them carefully 

 that their true nature was revealed. One is tempted, when doing syste- 

 matic work on any group, to pronounce each new form that meets his 

 eyes the most remarkable of all. I have become accustomed to having 

 my first notions, with regard to these soft-bodied forms, rudely shaken 

 by more careful subsequent study, but I think I have never encountered 

 any forms of entozoa that have proved to be so different from first con- 

 ceptions as these have done. 



In the first place the worms are quite small. The longest living 

 specimen that was measured was less than 5 mm . They must grow 

 somewhat longer than this, however, as an alcoholic specimen has been 

 found which measured 6 mm . The chains of joints that remain attached 

 to the heads of alcoholic specimens are few of them as much as 2 mm in 

 length. The head is of various shapes. When the tentacular probos- 



