328 M. C. Mereschkowsky on the Hydroida. 
the tentacle only by a very thin peduncle (Pl. XV. fig. 10). 
In the interior there was to be seen a yellowish mass, the 
nature of which could not be ascertained by M. N. Wagner. 
At the same time the surface of this little sphere or protube- 
rance gave origin in its turn to cylindrical pseudopodia, 
exactly of the same kind as those which were produced by 
the surface of the tentacles. These protuberances move 
slowly, and are put forth and disappear under the eyes of the 
observer. M. N. Wagner has communicated to me the inter- 
esting fact that, on making thin sections across the brain of 
the frog, previously hardened by freezing, it has keen observed 
under the microscope that after the nervous substance was 
thawed, it began to move after the fashion of the Am@be, and 
thus changed its place, just in the same way as the protube- 
rances of Oorhiza which I have just described. M. N. 
Wagener thinks that there is an analogy between these two 
facts, and supposes that these protuberances may be of a 
nervous nature, although certainly but little differentiated. 
In one of the ends of tentacles of Oorhiza figured by M. 
Wagner, I observe the presence of pigment dispersed in the 
form of red granules of different sizes among the trichocysts 
(Pl. XV. fig. 9). The presence of these in a spot to which 
they could not be conveyed by the current of digestive fluid 
(they are placed principally close to the surface of the end of 
the tentacle), as also their habit, which greatly reminds us of 
the pigments which are met with in the eyes of the Meduse 
(e. g. Syncoryne Sarsiz), leads me to believe that we really 
have to do here with the first commencement of the organ of 
sight, which certainly could hardly choose a better place than 
the tips of the tentacles. This explanation of the pigment 
in question is placed absolutely beyond doubt and has become 
a proven fact for every one who has read the brilliant article, 
“ Die Organ-Anfinge: I. Seh-Organ,” by M. G. Jiger, 
which appeared in the second part of the new German perio- 
dical ‘Cosmos’ *. M. Jiger treats the question of the forms 
under which the organs of sight must appear in the animal 
kingdom, and proves with marvellous clearness that the first 
indications.of these organs must consist in a part of the proto- 
plasm becoming pigmented (red, green, &c., and subsequently 
black), which retains the light and transforms the molecular 
movement produced by it into sensation of light, while the 
non-pigmented protoplasm, allowing all the light to pass 
through it, cannot feel the sensation of light. Thus not 
* Cosmos: Zeitschrift fiir einheitliche Weltanschauung auf Grund der 
Entwickelungslehre in Verbindung mit Ch. Darwin und E. Hickel, 1877, 
May, p. 94. 
