854 THE ANIMAL KINGDOM. 



sometimes a constant feeble light. The seat of the phosphorescence is 

 said to be the superficial layer of protoplasm. 



Leptodiscus medusoides has the form of a shallow concavo-convex disc 

 6-1 '5 mm. in diameter. It swims vigorously by contraction of the disc 

 into a bell-like form, the contraction including the whole disc ; a portion 

 only or two opposite portions of its circumference, however, may be thus 

 affected. 



The disc thins away towards its periphery, and a circular line of 

 granules divides it on its concave aspect into a central and peripheral 

 portion. There are two tubular depressions on the convex aspect, one 

 wide, the other narrow, both inclined obliquely towards the centre of the 

 concave side where lies a central mass of protoplasm inclosing the nucleus. 

 A bundle of parallel protoplasmic fibres extends to the base of the wide 

 depression. The narrow depression, however, reaches the central mass 

 and gives exit to a fine flagellum. There is said to be a distinct cuticular 

 membrane, thicker on the convex side where it is interrupted by the 

 apertures of the two depressions above-mentioned. Branching and anas- 

 tomosing cords of protoplasm radiate from the central mass to the 

 periphery on the concave aspect of the disc, and the gaps between the 

 larger branches are filled by a finer network. Branching cords extend 

 from the central mass and its central radial outrunners to the convex 

 aspect of the disc ; the corresponding extensions arising towards the 

 periphery are unbranched. The ends of these cords are attached each 

 to a small rod-like body placed vertically to the surface, possibly an 

 internal projection of the cuticular membrane. The intervals between the 

 cords are filled by a clear jelly. Fine radial fibres, supposed to be con- 

 tractile, stretch from the circular line of granules (stipra) to the centre. 

 Supposed fission-forms have been described by Hertwig, but nothing is 

 known as to the reproduction of the organism *. 



The Mastigophora are classified by Biitschli as follows : 

 I. Flagellata : animal provided with one or more vibratile flagella ; subdivisible 

 into four orders. 



1. Monadina : small or very small in size, and simple in structure ; naked 

 and very frequently more or less amoeboid ; sometimes furnished, however, with a 

 theca ; for the most part colourless ; chromatophores rare ; a single large anterior 

 flagellum and sometimes 1-2 small accessory flagella ; special oral aperture absent 

 or situate at the base of the flagellum, but never prolonged into a well-developed 

 oesophagus; includes five families, Rhizomastigina (ante, p. 841); Cercomonadina, 

 e.g. Oikomonas ; Codonoecina ; Bicoecina, e.g. Bicosoeca, Poteriodendron ; Hetero- 

 monadina, e.g. Monas, Dendromonas, Anthophysa, Dinobryon, Uroglena. 



2. Euglenoidina : in general large and well-developed ; with one, rarely two> 



1 Biitschli thinks (Protozoa, pp. 1078-9) that the Gymnodinium pseudonoctiluca, described by 

 Pouchet, Journal de 1'Anat. et Physiol. xxi, pp. 71-5, is possibly a spore-form of Leptodiscus. 



