270 GENERAL HISTOET OF THE INFT7S0EIA. 



gescMchte cler Turhellarien, 1851, p. 67), of a granular germ-mass in Ojmlina 

 Planariarum, at the posterior extremity of the animalcule, was nothing more 

 than the act of fission misconceived. The granular contents of the nucleus 

 (says Stein) are finer or coarser in the animals iiTespective of their size ; and 

 the supposed germinal masses, as the figiu^e given shows, were merely the 

 segments of the nucleus in process of di\ision, and not illustrations of the 

 ulterior development of that organ into other beings. Schultze witnessed 

 this process but once, in a specimen he named Opalina polymorplia, but which 

 was the same as the 0. Flanariarum of Siebold and Stein. 



Habitats, Vital Endowments, &c. — As stated before, the Opalincea are pa- 

 rasites of various animals, the most common of which are frogs, newts, and 

 other Batrachia, earth-worms {Lumhrici), some shell-fish, as the Anodon and 

 the common muscle {Mytilus eduUs), and of Planarke and several Entozoa. 

 They are found in the intestines in the earth-worm, in the rectum and bladder 

 in the frog, among the ciha of the tongue of that reptile, or among those of 

 the gills in the shell-fish, &c. 



As a memorandum touching the vital properties of Opalincea, we may quote 

 here an experiment made by Kolliker on the vitality and development of the 

 spermatic filaments {J. M. S. 1855, p. 298) : — '' The OpcdiiKB move in a solu- 

 tion of common salt of 1 per cent., and of phosphate of soda of the strength 

 of from 5 to 10 per cent. In a solution of salt of 5 per cent., and of sugar of 

 from 10 to 15 per cent., they shrink up and become quiescent, though re\'iving 

 upon the addition of water. I have even succeeded in reviving the Ojpalince after 

 they had been treated vnXh. a solution of common salt in the proportion of 

 one-tenth." 



Nature of Opalin-f:a. — The observations of microscopists in general concui' 

 to prove that these simple beings are not independent, but the mere embry- 

 onic or transitional phases of other animals. This opinion was put forward 

 by Schultze, and has been seconded by Agassiz, Stein, and others. 



Agassiz asserts (Silliman's American Journal, 1853) that the deficient Hnk 

 in Steenstrup's history of the succession of alternate generations of Cercaria, 

 and its metamorphosis into Distoma, is supplied by his discovery that a ge- 

 nuine Opal'um is hatched from the eggs of Distoma. Stein coincides also in 

 considering them metamorphosed into Vermes, and states that Steenstrup has 

 watched the transformation of Leuwjyhrj/s anodonta (Ehr.) into an intestinal 

 worm. He saw first that the cilia vanished, that they fixed themselves, and 

 became by-and-by changed into oval motionless bodies, which continued to 

 grow, and formed an internal space, within which a germinal mass was de- 

 veloped, out of which Cercaria originated. 



Affinities and Classification of Opaline: a. — Upon this head the first 

 point is to settle what genera and species are to be numbered with the Opali- 

 ncea. For our part we are chsposed to place in this family all Cihata which 

 are mouthless, andAvhich lead a parasitic life. As already noted, the absence of 

 a mouth is indicative of an embiyonic character, an indication strengthened, 

 if not confirmed, by observation ; consequently this group of beings is at best 

 but provisional, serving only the purposes of definition and nomenclature, 

 until science shaU be enabled to indicate the particular animals into whose 

 cycle of life they severally enter. 



Furthermore, we have seen that some reputed species are, in all probability, 

 only drfferent stages of existence of the same Opalina, — for instance, the 0. 

 armcita a more adult state of 0. Lumhrici. And, again, the stnictural differ- 

 ences between 0. iincinata and 0. Planariarum (consisting in the possession 

 of a singular pulsating vessel) and the rest of the group are so stiiking, that 

 they can scarcely be rightly included in one genus. 



