102 



HARDWICKE'S SCIENCE-GOSSIP. 



Each zooid is pear-shaped, with a slightly pointed 

 tail. The anterior part, the broader, is slightly 

 indented, and from this the flagella spring. Usually 

 there is one large granule in the interior. Stained 

 with iodine, these organisms are seen to have ;two 

 flagella, often of unequal length. The vibrations of 

 these organs produce in the colony a rotatory move- 

 ment. The zooids may be often found free. 



11. Anthophysa Miillcri (Fig. 54/, g, h). The 

 zooids of Anthophysa resemble those of Uvella, but 

 have only one flagellum. They are formed on a 

 branching stalk of a brownish hue, and occasionally 

 they get free from this and are then seen swimming 

 freely about. The stalks are sometimes so numerous 

 that they give a brown colour to pond-water. 



12. Bodo socialis is also another small sociable 

 infusorian found in pond-water. 



With regard to the two forms Codosiga and Dino- 

 bryon, I have never properly examined them, and so 

 will omit them here. 



13. Noctiluca miliaris is the largest of the Flagel- 

 lata. It is the common cause of the beautiful phos- 

 phorescence of our sea in summer-time. The organism 

 is easily visible to the naked eye. It is somewhat 

 kidney-shaped, one end is cleft, and from the top of 

 this there issues a large thick flagellum, striated 

 transversely. At the base of this is a tooth, and 

 below the tooth a delicate tiny flagellum. The net- 

 work of protoplasm is very distinct, and the nucleus 

 may be seen, together with large food-vacuoles or 

 "stomachs," which often contain large diatoms. 



OLIO FLAGELLATA. 



Of this division of the Infusoria, which may be 

 supposed to be a transition-stage between the Flagel- 

 lata and the Ciliata, only one representative is here 

 briefly introduced. 



14. Peridinium cinctum (Fig. 54 ;') is a member of 

 this family. It is divided by a constriction into two 

 halves, each furnished with a case or lorica, which, 

 like the silicious covering of the diatom, is beautifully 

 sculptured. From the constriction appear the cilia, 

 and from the apex the flagellum. This organism is 

 gTeen in colour, and resembles to a certain degree the 

 larval form of some of the worm family. 



Glenodinium and Ceratium also belong to the Cilio- 

 flagellata. The former is brown in colour and inhabits 

 fresh water, and the latter is phosporescent and marine 



The higher members of the Infusoria now occupy 

 our attention. This forms the third family, and is 

 known as the Ciliata. 



CILIATA. 



The large size of these organisms and their common 

 occurrence render them admirably suited for micro- 

 scopic study. They exist in great diversity of form, 

 and they may be classified, as will be shown later, 

 according to the arrangement of the cilia. 



Instead of noting their general characters, however, 



it will suffice to first describe a typical species. 

 Accordingly we will begin with Paramecium aurdia, 

 merely mentioning that it is one of the holotrichous 

 Ciliata. 



15. Paramecium aurelia (Fig. 55) — the slipper-ani- 

 malcule — is a large free-swimming species ; its length 

 is about the hundredth of an inch. It is found in 

 pond-water, and though by no means uncommon, the 

 other Ciliata must not be mistaken for it. It is oval 

 in shape, slightly narrower in profile than front view. 

 At the anterior end it is folded near the mouth, and 

 this gives it its slipper-like shape. 



The cilia are strong and arise from depressions in 

 the ectosarc, which is fairly thick and tough. The 

 roots of these cilia can be seen ,for some distance 

 piercing its outer layer, and this gives it a striated 

 appearance. When in motion they move so rapidly 

 that they cannot be seen, their rate is slackened or 

 accelerated, and often some are moving while others 

 are at rest. 



At this point it may not be out of place to define 

 briefly what a cilium is. It is a lash-like organ, a 

 fine filament, difficult often to see both from its 

 motility, and also from the slight density of its 

 substance, which seems little greater than that of 

 water. If we watch a row of cilia in action we see a 

 wave produced. This is because the cilia do not 

 move quite at the same time, but follow each other 

 after an imperceptible interval. The action of a 

 cilium is like that of a lash which moves sharply 

 downwards and then returns more slowly back 

 to an upright position. Hence, by their united 

 action, a current is produced which may be used 

 either for locomotion — as in the cilia which cover 

 the surface — or to produce a current for food — as in 

 those which line the cesophagus. 



The most superficial layer of the ectosarc is the 

 firmest and in some Ciliata becomes a hardened 

 cuticle or exudation layer (Fig. 55). Beneath this 

 the remainder of the ectosarc is called the cortex and 

 divided into three layers. First the layer which gives 

 rise to the cilia known as the ciliary layer, next the 

 muscular or myophan layer, lastly, the deepest layer, 

 which in some Infusoria contains thread-cells similar 

 to, but much smaller than the thread-cells (trichocysts) 

 of the Hydra. The ectosarc, then, is by no means so 

 simple as in Amceba, but it must be understood that 

 these layers are not clearly defined one from another. 

 The inner protoplasm or endosarc is more fluid and 

 exhibits a rotation or streaming of the particles which 

 it contains. This is best studied in Paramecium 

 bursaria. 



There are two contractile spaces situated one near 

 each end, probably in the deepest layers of the 

 ectosarc. At first one is inclined to confuse these 

 with the numerous food-vacuoles present in various 

 parts of the endosarc, but by carefully watching, the 

 spaces are seen to disappear and then slowly reappear. 

 The disappearance of the vesicle is called its systole, 



