366 



NATURAL BISTORT. 



F'g. 18 TBI- 



CHONOMORPHA 



AGII.IS. (Leidy) 



ranarum, ^V 



decayed wood, and the filaments of one of the Alga?. Trichonomorpha agilis (Fig. 18) has the cilia 

 various in length, forming three or four distinct sets, and one of them is very long. The body is 

 more or less separable into a smaller ovate head-like portion and a larger and inflated body. 

 The oral aperture is indistinct, and is a rounded pore at the summit of the head, whence there 

 passes backwards a tube to the eiidoplasm of the posterior part. There is a granular 

 nucleus in the centre, but no contractile vesicle has been observed. The movements 

 consist of an incessant retraction or shortening and bending to and fro of the head-like 

 anterior region, accompanied by the rapid waving and swelling outwards of the long 

 cilia. It is very possible that these animals may belong to another class of animals 

 altogether. 



The last group of the Holotrichous Ciliata contains one family, the Opalinidae. 

 whose species are parasitic within the intestines of Amphibia and Invertebrata. The 

 genus Opalina is very characteristic, and its species are mouthless, free-swimming, and 

 they may be ovate or elongate in shape. The cilia cover the cuticle throughout, 

 and this is striated. There are no extraordinary organs of prehension, and the 

 spherical or oval endcplast is single in young individuals. It breaks up by repeated 

 divisions, as growth proceeds, into innumerable minute rounded bodies, each having 

 a clear peripheral zone and endoplastule. There is no contractile vesicle. Opalina 

 i to Jgth of an inch long, is found in the intestines and rectum of the common frog and 

 toad. Its body is usually ovate, flattened, evenly rounded posteriorly, and the anterior part 

 is bluntly pointed. The minute embryos contained in cysts (Fig. 19, G) are found in the rectum 

 and excreta of frogs in the early part of the year. They get into the water where tadpoles are 

 developing, and are eaten by them. The cyst has its wall broken or dissolved in the digestive canal 

 of the tadpole, and the embryo is set free. At this stage the young Opalina is long, 

 egg-shaped, covered with cilia, and has a large endoplast and a number of corpuscles in the 

 endoplasm (Fig. 19, H). After a short interval, the body becomes longer, slightly curved in front, 

 and the endoplast becomes divided into two or four equal spheroidal portions (Fig. 19, i). After 

 a while the pointed end becomes 

 rounded, and the normal shape is 

 attained (Fig. 19, A). When fully 

 grown the animalcule begins to 

 increase in numbers by fission, 

 and the first division takes place 

 obliquely (Fig. 19, B), so that one in- 

 dividual has a pointed posterior end, 

 and the other a rounded-off one. 

 The separated moieties subdivide 

 over and over again, first obliquely 

 and then transversely (Fig. 19, c, D), 

 until at last the pieces are not 

 more than ^ 7 th to y^oth of an 

 inch in length. These are long, oval 

 in shape (Fig. 19, F), and soon 

 become languid in their movements, and contract to a spherical shape, diminishing in bulk and 

 becoming encysted. The encloplasts included in the animal at the encystment unite in one, after the 

 swallowing by the tadpole, and this one is carried out with the young free-swimmer. 



Another genus of the Opalinida? is Anoplophrya, and 

 its species are parasitic within the intestinal organs of many 

 Invertebrata. The type is Anoplophrya prolifera (Fig. 20), 

 which is found in the intestinal cavities of various marine 

 Annelids on the Norwegian coast. It is mouthless, long, widest 

 in front, striated longitudinally, and ciliated along the striae. 

 The endoplast is in the axis, is long and sub-cylindrical, and the contractile vesicles ai*e numerous, 



Fig. 19. OPALINA RANARUM. (After Zeller and Englemann.) 



A. Adult. B. Oblique division c, Transverse fission, n. Fission. F, Last stasre before 



encystment. o, H, I, J, Stages of growth of young. 



Fig. 20. AXOl'LOPHRYA PKOLIFEKA. 

 (After Claparede and Laclimann.) 



