180 
Becent Progress in our Knowledge of 
the end on whicli the mouth is situated ; a short stem hecomes here 
developed, and the ciha wreath gradually disappears. Then upon 
the free end the peristome and cilia disk make their appearance, and 
the growth of the stem completes the development. 
Everts remarks that in this process we have an example of 
alternation of generations. There is one point, however, in which 
he has overlooked its essential difference from a true alternation of 
generations, namely, the ahsence of any intercalation of a proper 
sexual reproduction. 
Kay Lankester * has suhjected to spectrum analysis the blue 
colouring matter of Stentor cmruleus. This occurs in the form of 
minute granules in the cortical layer of the animal, and Lankester 
finds that it gives two strong absorption bands of remarkable 
intensity, considering the small quantity of the matter which can 
be submitted to examination. He cannot identify these bands 
with those of any other organic colouring matter, and to the 
peculiar pigment in which he finds them he gives the name of 
stentorin. 
He has also examined the bright green colouring matter of 
Stentor Mulleri, and finds that instead of giving the stentorin 
absorption bands, it gives a single band Hke that of the chloro- 
phylloid matter of Hydra viridis and of Spongilla. 
Eay Lankester t has also described, under the name of Torqua- 
tella fypica (Fig. 3), a remarkable marine Infusorium, which, though 
quite destitute of true cilia, can scarcely be separated from the 
proper Ciliata. With the general structure of the cihate Infusoria, 
the place of a peristomal cilia wreath is taken by a singular plicated 
membrane, which forms a wide, frill-like, very mobile appendage, 
surrounding the oral end of the animal, and projecting to a con- 
siderable distance beyond it. The author regards Torquatella 
ty]pica as the type of a distinct section of the Ciliata to which he 
gives the name of Galyeata. 
Of all the authors who since Yon Siebold have applied them- 
selves to the investigation of the Infusoria, Haeckel must be men- 
tioned as the one who has brought the greatest amount of evidence 
to bear on the question of their unicellularity. In a very elaborate 
paper which has quite recently appeared, J and which is remarkable 
for the clearness and logical acuteness with which the whole subject 
is treated, Prof. Haeckel, resting mainly on the observations of 
others, and partly also on his own, argues in favour of the 
unicellularity of the Infusoria from the evidence afforded both by 
the phenomena of their development and by the structure of the 
mature organism. He confines himself chiefly to the Ciliata — 
* ' Quart. Journ. Mic. Sci.,' 1873. t ibid., 1874. 
X Haeckel, "Zur Morphologic der Infusorien," Jenaisclie Zeitschr., Band vii. 
heft 4, 1873. 
