ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 77 



Protozoa. 



Erythropsis agilis, a New Protozoon.* — R. Hertwig gives an 

 account of a Protozoon remarkable for the high degree of its organiza- 

 tion, and by the undoubted possession of a pigment-spot, which he 

 cannot refuse to regard as an eye. He was unfortunately unable to 

 find more than a single specimen, which he found when studying the 

 development of the eggs of Echinoids. Its external appearance is 

 that of an Appendicidaria, for it has a longish rounded body which is 

 continued into a very contractile tail-like process. 



Like that of the Infusoria, the body of Erythropsis is asymmetrical, 

 and an anterior can be distinguished from a posterior, a right from a 

 left, and a dorsal from a ventral surface. Yentrally there is a 

 deep groove, which is deepest about the middle of the body, and 

 becomes shallower towards either end. To the left of it is a pigment- 

 spot, to the right a sporophor, and at its base the pigment-spiral. 

 Anteriorly it is overlaid by the opercular apparatus, and from its 

 hinder end there arises the caudal appendage. 



The greater part of the body consists of solid protoplasm, alto- 

 gether free of vacuoles, and having a number of coarser and finer 

 granules scattered in it ; among these there are many intensely 

 coloured reddish-brown pigment- granules, a rod-like structure resem- 

 bling bacteria and of a high refractive power. The structureless 

 cuticle has a double contour. The eye of the observer is sure to be 

 most attracted by the pigment-spot, in the centre of which there is a 

 spherical body which calls to mind an otolith or even a lens ; which 

 latter name, indeed, Hertwig applies to it. During life it appeared 

 to be completely homogeneous and highly refractive. The sporophor 

 has its investing cuticle well developed and marked by fine ridges. 

 Near it is a spiral filament about which Hertwig doubted whether it 

 was a simple cuticular structure, or whether it was contractile. 



The nucleus, which was coloured intensely red by picro-carmine, 

 was seen to have the peripheral parts of its framework continued into 

 a layer of fine and homogeneous granules. The cylindrical tail was, 

 when most extended, three or four times as long as the body, and, 

 when contracted, twice as long ; its substance was homogeneous, 

 highly refractive, and called to mind the stalk-muscle of the Vorti- 

 cellidse ; it is a very powerful locomotor organ and enables its 

 possessor to move rapidly through the water ; it had no contained 

 spiral. 



Taking into consideration the high organization of Erythropsis we 

 cannot wonder at Hertwig's doubts as to whether it really does belong 

 to the Protozoa ; a positive proof is afforded by the presence of a 

 single large nucleus, and by its reactions, and a negative one by the 

 complete absence of any other nuclei, the presence of which would, 

 on account of the transparency of the protoplasm, have hardly escaped 

 a careful search. 



The pigment-spot must not only be supposed to be an eye, but 

 also to have nearly the same optical power as the ocelli of many 



* Morph. Jahrb., x. (1884) pp. 204-13 (1 pi.)- 



