THE MASTIGOPHORA 279 



The best known form is the common Noctiluca mttiaris of our coasts. The 

 adult Noctiluca is about the size of an ordinary pin's head (1 to 1'5 millimetres 

 in diameter). The spherical body consists chiefly of jelly, with at one pole 

 a superficial concentration of the protoplasm containing the nuclei and giving 

 off the locomotor organs. Prom this central mass of protoplasm strands extend 

 in an irregular network through the whole body, which is limited by a thin 

 pellicle. The central protoplasm bears the so-called " peristome," a deep groove 

 containing the mouth-aperture near one end. The mouth is bordered by pro- 

 jections known as the " tooth " and the " lip," and near it arise two motile 

 organs a small flagellum, and a large tentacle-like process which shows a 

 transversely striated structure and performs twisting and lashing movements. 

 The tentacle is sometimes named the " flagellum," and the true flagellum 

 the " cilium " ; the former probably serves as the organ of locomotion, the latter 

 for food-capture. The nutrition is holozoic. 



Noctiluca reproduces itself by binary fission, and also by multiple fission 

 producing a brood of small flagellate swarm-spores. The formation of the latter 

 has been stated to be preceded by isogamous conjugation of the adults, but 

 the matter is open to doubt, and it is possible that the swarm-spores them- 

 selves represent the gametes. Other genera of Cystoflagellata are Leptodiscus 

 and Craspedotdla (Kofoid, 373), both remarkable for their superficial resem- 

 blance to medusae. No tentacle like that of Noctiluca is present in either of these 

 forms, and locomotion is effected by rhythmic contractions of the disc-like 

 body. 



Bibliography. For references see p. 486. 



