278 MR J. T. CUNNINGHAM ON 



The cysts vary in size with the age and size of the worm within, and the 

 youngest and smallest ones are brittle and dark brown in colour. A very 

 young worm taken from such a cyst is shown in fig. 4. It has only seven 

 suckers. The worm in all cases, when placed on a slide in a little water, 

 exhibits movements of contraction and extension, and coils or straightens its 

 body, but is not able to travel over much space. When an infected crayfish is 

 opened which has been twenty-four hours out of water, the worms are often 

 found to have escaped from the cyst, and are found lying on the muscles ; but 

 I think this does not take place while the Nephrops is living. The number of 

 c}*sts varies considerably. I have sometimes found them covering the posterior 

 part of the intestine completely; and in other cases only two or three of the 

 very smallest brown cysts were present. The diameter of the cysts varies from 

 •5 mm. to 2 or 3 mm. I have taken as many as forty worms from a single 

 Nephrops. 



The proportion of specimens of Nephrops infected is not small. In one 

 case I found three out of eight contained the parasite. Usually out of a dozen 

 opened three or four are infected ; but sometimes a dozen may be searched 

 without a single parasite being found. My observations have extended now 

 over nearly four months, and I have not yet found any variations in the state of 

 the parasite. 



I have not found the parasite in any other part of the body of Nephrops 

 except the intestine ; and I have no evidence to show whence it is derived, 

 what is its mature state, or in what conditions its adult stage is passed. 



It seems probable that the eggs are taken into the stomach of Nephrops 

 with its food, and that an embryo escapes from the egg, which pierces the wall 

 of the intestine, and there develops into the stage of the worm which I have 

 examined. The further development most likely takes place in the body of 

 some large fish which feeds on Nephrops ; but hitherto no Trematode is known 

 living inside the body of a marine fish except the Calicotyle Kroyeri, which is 

 found in the cloaca of rays, and Encotyttabe Pagelli in the mouth of Pagelhis 

 centrodontus* 



In passing on to consider the affinities of the parasite, it may be set down 

 as obvious that it is in every respect a typical Trematode. The characters of 

 the water-vessel system and of the suckers could not be found outside that 

 class. But the arrangement of the suckers is entirely novel. A serial arrange- 

 ment of the suckers is not uncommon among Trematodes ; but there is no 

 other genus in which they form a single series extending along the median 

 ventral line through nearly the whole length of the body. The series when 

 present is usually double. Microcotyle t has in the posterior third of its body 



* Van Beneden et Hesse, Mem. Acad. Boy. de Belg., Torn, xxxiv. 

 t Ibid. 



