MIDLAND NATURALIST. 13 
however, confined to the protoplasmic interior. A bundle of fibres 
starting from the central mass of protoplasm around the nucleus 
is very evident, and these become abruptly striated in the tentacle. 
Special emphasis should be laid on this fact, as it is a direct proof 
of Prof. Carnoy’s view concerning the physiological role that the 
reticulum of the protoplasm performs in the life functions. : Accord- 
ing to him, “the reticulum of the protoplasm is the sole seat of 
irritability and contractility, and it alone determines the physical 
movements of living things.” * e see in this tentacle 
with its striated structure a transformation of reticulum into a 
muscle fibrilla. 
From a phylogenetic point of view we might call attention 
to the similarity of the structure of the tentacle of Noctiluca to the 
stalk of a Vorticella. Such questions as the following might be 
asked: “Might not the ancestral forms of Notciluca have been fixed 
by a stalk like Vorticella? Is Noctiluca a freed Vorticella with the 
stalk persisting as a tentacle and still exhibiting the same structure? 
In other words, has Noctiluca the same ancestral formsas Vorticella >” 
These are questions that intrude themselves on our mind while we 
study the structure of Noctiluca and particularly of its tentacle. 
In Vorticella the stalk is the organ of motion, the cilia being used 
only to convey the food to its mouth. As long asthe stalk isfixedat 
its distal end, the motion of the animal is limited, and it is necessary 
that it have organs to bring food to the mouth. In Noctiluca the 
stalk being freed from its permanent attachment it becomes an 
organ of free motion. The crown of circumoral cilia, therefore, 
becomes useless, degenerates, only a single cilium remaining to 
trace the ancestral relationship. Close to the mouth of the animal 
and between it and the tentacle, is noticed a zigzag line which 
Huxley called the tooth, and near it a small lobule called the lip 
from which arises the solitary remaining cilium which is seldom 
seen in preserved material. Near this is the slit-like opening, the 
mouth, leading into the interior of the central protoplasm. All the 
structures just mentioned are situated in the buccal groove. From 
the end of the buccal groove a string of fibrillar protoplasm extends 
for some distance farther and produces a raised ridge (Fig. 2, H). 
This is the rod, the function of which is not known. 
After thus completing the study of the external anatomy of ` 
Noctiluca, we may penetrate into the labyrinth of its internal 
structure. Immediately under the cuticle we see as represented in 
* Carnoy.—Biologie Cellulaire page 196. 
