852 THE ANIMAL KINGDOM. 



(iv.) Cystoflagellata s. Rhynchoflagellata. Two genera, both marine, 

 are contained in this sub-class : Noctiluca with probably only one species, 

 N. miliaris, which is widely distributed, and Leptodiscus medusoides, found 

 by R. Hertwig at Messina. In both genera the protoplasm is broken up 

 into a central mass with branching cords extending from it. 



Noctiluca is from one point of view globular, from another at right 

 angles to the first, somewhat kidney-shaped. It is divisible into two 

 halves, a right and left. In the median plane is an elongated depression, 

 the peristome, at the base of which is a slit-like mouth. At one end, the 

 anterior, of the peristome is a flat tentacle, and close behind it on the 

 right side two small ridges one behind the other, one ending in three or 

 four points, the tooth, the other somewhat semicircular in outline, the lip. 

 A flagellum is inserted at the anterior end of the lip. Each margin of the 

 posterior end of the peristome is bordered by a slight fold ; the two 

 folds approach one another and are continued onwards behind the peri- 

 stome as the * staff-organ/ until they meet at a point corresponding to one 

 end of a diameter, which joins at its other end the anterior border of the 

 peristome. In size the animal may attain -5-1 mm. (^ in.) or even more 

 (Giglioli). 



The surface of the body is covered by a delicate clear layer, the 

 cuticle of some authors, which is probably a superficial stratum of the 

 protoplasm differing somewhat from the rest in physical and chemical 

 characters. A mass of protoplasm containing the nucleus lies beneath the 

 peristome, the mouth opening directly into it. From this mass radiate 

 branching and anastomosing cords, their fine ends ending in a thin super- 

 ficial layer. The cords are separated by large vacuoles ; they contain, as 

 does also the superficial layer, small non-contractile vacuoles, and 

 they show a slow movement of granules. Special cords of protoplasm 

 pass to the tentacle, tooth, lip, and staff-organ. The food is always 

 inclosed in a food vacuole. The nucleus is oval or round, and possesses 

 a distinct nuclear membrane. The tentacle is slightly concave on one 

 side, convex on the other. Its movements are slow ; it can be extended, 

 contracted, or rolled up towards its concave aspect, but does not seem to 

 subserve locomotion. It usually attains a length of about half the diameter 

 of the body. Structurally, it consists of a delicate membrane-like invest- 

 ment filled by an extension of the protoplasm. The concave side is 

 transversely striate owing to a parallel arrangement of the bands of proto- 

 plasm 1 . The tooth, which is yellowish in colour, the lip, and flagellum 

 are also extensions of the protoplasm. The movements of the flagellum 



1 The tentacle is said by Vignal to resemble physiologically a muscle. It contracts at the 

 opening and closure of a constant current, and passes into tetanus lasting 3-4 minutes under an in- 

 terrupted current. It ceases to contract spontaneously when poisoned by curari, but remains electri- 

 cally excitable. See Vignal, Arch, de Physiol. norm, et patholog. (2), v. 1878. 



