BROOKS AND RITTENHOUSE: ON TURRITOPSIS. 435 



illustrates a section through the base of a tentacle, /, 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; f 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. poli/nema from the Atlantic coast of France; 

 T. nuiricula 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 1SS6. 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 







