40 



LOWER INVERTEBRATES. 



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

 mecia increase by transverse fission. The cortical layer 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 Jounial of the Royal 

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

 have various forms and dispositions in different species. Some xegard them as ho- 

 mologous with t\\c thread-cells of the Coelenterata, and as having a similar function ; 

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

 schwartzii, which has trichocysts entu-ely similar to the thread-cells of 

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

 trichocysts are in-egularly disposed, Kent suggests that they may be 

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

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

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

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

 P- bursaria is usually colored green by chlorophyll granules, — now 

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

 FiG. si'-Parame- -yyater sponges, and the common green Hydra. Owing to the presence 

 magaifled 250 ^f tjjg green corpuscles the circulation of the endoplasm is seen to 

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

 are forms like VorticeUce 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 not 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 possibly are to be considered as ovules. 



Amono- the most curious of ciliate Infusoria those of the family Trachelocebid^ 

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



a long flexible neck, with the oral 

 aperture at its terminus. Trache- 

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

 group ; it appears to be cosmopolitan, 

 occurring among algae in ponds and 

 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 implies, affords 

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

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

 tion of the branches. AmpMleptus gigas 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 

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



Fig. 39. — Trachelocera olor, enlarged 375 times, u. Contractile 

 vesicle, m. Mouth, n. Nucleus. 



