BROOKS AND RITTENHOUSE: ON TURRITOPSIS. 435 
illustrates a section through the base of a tentacle, t, and shows that the 
tentacular chorda-like endoderm, which is so common in the tentacles 
of hydroids and hydroid jellyfishes, is of the same character as that of 
the radiating canals of Turritopsis. The velum is shown in this 
figure at v; the velar nerve ring at n 1 ; the tentacular nerve ring, 
which innervates the visual organs, at n 2; / is the ectoderm of the 
subumbrella; b that of the exumbrella; and d the endodermal lamella. 
Figures 1, 2, 3, and 5 (pi. 30), are a series of successive sections 
through the stomach and proboscis. The reproductive organs are 
shown in cross section in plate 30, figure 1, and in side view in plate 
30, figure 4. They are, no doubt, fundamentally radial, but the 
halves are pushed apart by the channels through which the radiating 
canals open into the stomach, so that each half joins the half of the 
adjacent reproductive organ in the interradial plane. There are, in 
effect, four interradial gonads, although each is to be regarded as the 
halves of two perradial gonads. Four vertical interradial furrows, 
shown at e in the section, and shown much more plainly in the older 
medusa that is represented in figure 4 (pi. 30), indicate the planes in 
which this secondary union is to be regarded as having taken place. 
Haeckel recognizes four species of Turritopsis: T. armata from the 
Mediterranean; T. polynema from the Atlantic coast of France; 
T. nutricula from the Atlantic coast of North America; and T. pleuro- 
stoma from the coast of Australia. 
A number of medusae, from various parts of the world, which are 
very similar to Turritopsis, have been described, and placed together 
in the genus Modeeria. They exhibit most of the distinctive charac¬ 
teristics of Turritopsis, in a much less pronounced condition, and they, 
no doubt, present these characteristics in their more primitive form. 
One of them is represented in plate 31, figure 8, which is from draw¬ 
ings made at Nassau in 1886. It closely resembles Turritopsis in 
habits and form, and the account of the habits and form of Turritopsis 
in the memoir of 1886 applies to it without any changes. It resembles 
Turritopsis in the way that the tentacles are carried; in the position 
of the ocelli, and in the suspension of the proboscis by a stalk of modi¬ 
fied, chorda-like, endoderm cells. The radiating canals communicate 
with the stomach by vertical grooves, as in Turritopsis, and the per¬ 
radial gonads are divided into halves by these grooves, but not so 
completely as in Turritopsis. The peduncle consists of the endoderm 
of the radial canals, as in Turritopsis, but the enlargements are not so 
