FLAGELLATA 



133 



eiices, of which one, a little firmer than the other, and trans- 

 versely ridged, is called the tooth ; at the junction of the two is 

 a second, minute, flagellum, usually called the cilium. Behind 

 these the oral groove has an oval space, the proper mouth; 

 behind this, again, the oral groove is continued for some way, 

 with a distinct rod-like ridge in its furrow. The whole body, 

 including the big flagellum, is coated by a strong cuticular 

 pellicle, except at the oblong 

 mouth, and the lips and 

 rod are mere thickenings 

 of this. The cytoplasm has 

 a reticulate arrangement : 

 the mouth opens into a 

 central aggregate, from 

 which strands diverge 

 branching as they recede 

 to the periphery, where 

 they pass into a continuous 

 lining for the cuticular 

 wall, liquid filling the 

 interspaces. The whole 

 arrangement is not unlike 

 that found in many plant- 

 cells, but the only other 

 Protists in which it occurs 

 are the Ciliata Trachelius (Fig. 56, p. 153) and Loxodes. The 

 central mass contains the large nucleus. Noctiluca is an animal 

 feeder, and expels its excreta through the mouth. The large 

 flagellum is remarkable for the transverse striation of its plasma, 

 especially on the ventral side. The cuticle may be moulted as 

 in the Dinoflagellates. As a prelude to fission the external 

 differentiations disappear, the nucleus divides in the plane of the 

 oral groove, and a meridional constriction parts the two halves, 

 the new external organs being regenerated. Conjugation occurs 

 also, the two organisms fusing by their oral region ; the loco- 

 motive organs and pharynx disappear ; the conjoined cytoplasms 

 unite to form a sphere, and the nuclei fuse to form a zygote 

 or fertilisation nucleus. This conjugation is followed by sporu- 

 Jation or brood-formation.^ 

 ' This process has the character of telolecithal segmentation in a Metazoan egg. 



Fig. 48. — JVoctSuca miliaris, a marine Cysto- 

 flagellate. (Prom Verivorn.) 



