40 LOWER INVERTEBRATES. 



that these phenomena are really due to abnormal pressure of the cover glass. Parob- 

 mecia increase by transverse fission. The cortical laj-er contains numerous vertically 

 disposed rod-like bodies called trichocysts. When a Paramecium is treated with very 

 dilute acetic acid these protrude from all parts of the surface, giving the animal the 

 appearance of being clothed with very long cilia. A solution of tannin in glycerine pro- 

 duces a similar effect, although it is claimed by a writer in the Journal of the Royal 

 Microscopical Society that it is due to a hardening of the cilia. These trichocysts 

 liave various forms and dispositions in different species. Some regard them as ho- 

 mologous with the thread-cells of the Co-lenterata, and as having a similar function ; 

 others regard them as tactile organs. Btitschli has described a species, Polykrikos 

 schicartzii, which has trichocysts entirely similar to the thread-cells of 

 the sea-anemone. Since this infusorian inhabits salt-water, and the 

 trichocysts are irregularly disposed, Kent suggests tliat they may be 

 thread-cells which have been swallowed. Paramecium bursaria (Fig. 

 38) is shorter and broader than P. aiirelia, and is less flattened ; the 

 buccal fossa is fuimel-shaped, extending obliquely from left to right. 

 The nucleus is oval and the nucleolus is attached to the side of it. 

 P. hursaria is usually colored green by chlorophyll granules, — now 

 held by some to be parasitic alg£e, as is also the green color of the fresh- 

 ^^^ci^iiin tersaria Water sponges, and the common green Hydra. Owing to the presence 

 ™^snified 250 Qf j}jg green corpuscles the cu-culation of the endoplasm is seen to 

 better advantage than, perhaps, in any other infusorian, although there 

 are forms like Vorticelloi which exhibit this phenomenon in a marked degree. This 

 rotation is uniform, ascending on the left side, and descending on the right, when seen 

 from above (indicated in the figure by the arrows). Balbiani has shown that the so- 

 called longitudinal fission is uot really a fission, but a phase of the act of conjugation. 

 Two animalcules may remain attached by their anterior extremities for several days; 

 after separation, the nucleus and nucleolus changes, the latter becoming more or less 

 striated, while the former breaks up into a variable number of spheroidal bodies, which 

 finally separate from the parent, and jjossibly are to be considered as ovules. 



Among the most curious of ciUate Infusoria those of the family Traciielocbrid.e 

 are entitled to the front rank. Their flask-sliaped bodies arc drawn out anteriorly into 



^ a long flexible neck, with the oi'al 

 i ,-. ^ aperture at its terminus. Trache- 

 locera olor (Fig. 39) is the tyjje of the 

 si>i^ gi"oup; it appears to be cosmopolitan, 



Fig. 39. -TracMoMmoiw, enlarged 376 times, c. Contractile occurring anions; al"£e in ponds and 

 vesicle, m. Mouth, n. Nucleus. ^ o o i 



Streams. Under examination in the 

 living state it appears to be incessantly exploring for food, thrusting its wonderfully ex- 

 tensile neck right and left into every cranny. As it swims gracefully through the water, 

 with a spiral motion, its form and attitude very naturally suggest the swan. In Lachry- 

 maria the neck is only slightly extensible. Maryna socialis, as its name hnplies, affords 

 an instance somewhat rare among the Holotricha, that is, the formation of a zoocytium. 

 Tins structure is branched like a tree, the cup-shaped zooids projecting from the termina- 

 tion of the branches. Amphileptus yigas is an elongate compressed animal, which may 

 easily be mistaken for a Trachelocera on account of its long neck, which assumes as 

 many shapes as in that genus ; it is readily distinguished, however, since the mouth in 

 Amphileptus is at the base rather than at the apex of the proboscis. It is said to feed 



