364 



NATURAL HISTORY. 



Invertebrata. They have tentacle-like processes, derived from the cuticle or from the endoplastn, 

 or from both of these parts. The body contains an endoplast and one or more contractile vesicles. 

 They increase Toy division across or longitudinally, and also by budding, which may be external or 

 internal. Some of the young (embryos), on escaping from the parent, are ciliated, and the cilia 

 may be arranged over the whole body, or in the form of a wreath around the body, or only on 

 the under surface. With growth the state changes, and the cilia are lost. Others resemble the 

 parent. The ad alts have neither cilia nor flagella. The majority of species are sedentary. 

 The Tentaculifera are divided into two sub-orders, in one (the Suctoria) the tentacles are wholly 

 or partially suctorial in their office, and in the other (the Actinaria) they are not suctorial but 

 merely adhesive. One family of the first sub-order has one or two tentacles only, and another 

 (the Acineta) has many tentacles, and some of the genera have the body without, and others with 

 a lorica or a more or less covering sheath. Acineta tuberosa has the tentacles in bundles, which 

 protrude through the transparent lorica, and the endoplasm can be seen within. It is a salt water 

 form, and measures from -^th to TUi7 tn of an inch in len g tn ( Fi g- 5 )- 



These animalcules remain with their tentacles extended, and other freely-swimming minute 

 Infusoria are stopped by the suckers at their tips. The endoplasm of the victim passes into 

 the hollow of the tentacle and mixes with the soft tissue of the body of the Acineta. A third 

 family includes the genus Dendrocometes, which settles on Gammarus pulex, and has rather flexible 

 tentacles slightly branched at their extremities. Its embryos, which escape from the parent, 

 are ciliated underneath only. The next family includes branching Acinetans, with many tentacles, a 



host of individuals apparently arising from a 

 common stem. But the tops of the ramified steiii 

 are really riot separate individuals, and the whole 

 mass must be looked upon as one (Fig. 6). 



Some embryos with tentacles are produced from 

 the ends of stems (Fig. 6, b), and those which are 

 ciliated are derived from the thicker parts of the 

 stem (Fig. 6, a). 



The endoplast is ribbon-like, and is much con- 

 torted in the stolon and band parts of the main stem, 

 and is continued as a band into the branchlets. 



The next sub-order (the Actinaria) have the ten- 

 tacles simple or ray-like, as in the family Ephalotidre, 

 or represented by one or more retractile organs, 

 which resemble a proboscis with or without cirri. 

 The genus Ophryodendron (Fig. 15) is the type of the 

 last, and the species are very extraorclinai-y-looking 

 things. The animalcules may be solitary or in 

 a little group, and then one has a long proboscis, 

 and the others are more or less vermiform or flask-shaped, with a delicate tubular ending. The 

 prey is caught on the proboscis, and gradually withdrawn into the body. They inhabit salt water, 

 or fix on to the polyparies of Hydrozoa, or on to Crustacea. The embryos are ciliated. 



ORDER CILIATA. 



In this order the animalcules are more or less covered with vibratile cilia, some of which may be 

 modified into seise, styles, and hooks or uncini. A well-developed oral and anal aperture is mostly present. 



The example (Paramecium aurelia) already given of this order brings these important characters 

 before the mind. The order is divided into four sub-orders, of which the first is the Holotricha, 

 or the Animalcules, which are closely covered all over with cilia, and usually furnished with 

 trichocysts. Paramecium is the example of the first family of the sub-order (Fig. 2). 



The Prorodontidse are the second family, and they are ovate or cylindrical, and the oral aperture 

 is at one end or at the side. The canal (pharynx) leading from the mouth to the endoplasm is 

 bounded by rod-like teeth, which are well seen in the genus Prorodon (Fig. 10). 



Fig. 15. A, OPHRYODENDRON PEDICELLATUM ON A 



PLUMULARIA STEM (THE ELONGATE FORMS ARE THE 

 VERMIFORM BODIES) ; B, MORE HIGHLY MAGNIFIED ; 

 C, O. MULTICAPTTATUM. (After Saville Kent.) 



