844 THE ANIMAL KINGDOM. 



ing phase, and rarely while it remains motile, its colour changes to red 

 owing to the formation of haematochrome dissolved in droplets of fat. 

 The formation begins centrally, and spreads to the periphery, disappearing 

 in the reverse direction. It masks the chromatophores when they do not, 

 as is sometimes the case, entirely vanish. Special red-specks, the eye 

 specks or stigmata, of a rounded or rod-like shape, simple, or when large 

 composite, are present to the number of one or more in most coloured 

 and in some colourless forms. They may be placed near the base of 

 the flagellum, the middle of the body ( Volvocina, some Chlamydomonads), 

 or even at its hinder end (other Chlamydomonads). A lens-like structure 

 is said to co-exist with the stigma in the Euglenoid P/iacus, and a colour- 

 less strongly refractile body in the position of a stigma in some colourless 

 forms, e. g. Monas. The function of the stigmata is doubtful, but they are 

 said to disappear in darkness. Forms devoid of them are said to react to 

 light in the same way as those which possess them. Trichocysts similar to 

 those of Infusoria, are lodged at the anterior end of the freshwater 

 Euglenoid Gonyostomum s. Merotricha semen ; their presence elsewhere is 

 doubtful. 



Reproduction takes place by fission in the free or encysted state, the 

 latter being frequently preceded by conjugation. Fission in the free state 

 may be binary, and it may be continued without an interval for the growth 

 of the progeny. It is sometimes transverse, but as a rule longitudinal. 

 It occurs while the organism is in the flagellate motile condition, rarely 

 when the flagella have been cast off, the organism remaining motile or 

 becoming motionless as in some Euglenina, or still more rarely when it is 

 amoeboid as in Ciliophrys, the two products in this case being flagellate. 

 Details vary, but fission of the organism itself occurs only after the 

 principal organs have been already doubled by division, or by new forma- 

 tion as is the case with the contractile vacuole, and sometimes with the 

 flagella even in longitudinal fission. Repeated fission takes place in some 

 Chlamydomads under the protection of the cuticle while the parent 

 organism is motile, and sometimes results in the formation of numerous 

 small individuals or microgonidia. The products are set free by rupture 

 of the cuticle which may be gelatinised previously. Encystation previous 

 to fission occurs in some species of Etiglena, &c. The cyst varies in 

 thickness and consistence ; fission within it is binary, sometimes continued 

 to 4-8 or even more, and the products of fission may grow, encyst, divide, 

 without assuming a free state ; consequently clusters of encysted forms are 

 frequently met with resembling the algal Pleurococctis. Microgonidia are 

 sometimes thus produced. 



The products of fission sometimes remain associated, or even or- 

 ganically connected, to form colonies. In Dinobryon and Poteriodendron 

 the young individual attaches itself to the edge of the parental cup. 



