252 BULLETIN OF THE 



more transparent. It wants also the brown red color of the well-known 

 Mediterranean species. 



Ocyroe crystallina, Rang. 



Plate I. Figs. 1-6. 



A larval stage of this medusa* was found at the Tortugas. The anatomy 

 of this Ctenophore is very characteristic. It differs from De'iopea kaloktenota, 

 Chun,f in size, in the absence of tentacles, and in the presence of very prominent 

 longitudinal muscles (I m) on the under and inner surface of the oral lappets. 

 It has only a remote likeness to the young of other genera. The motion of the 

 animal is very characteristic, as it is caused, for the most part, not by the 

 movement of the vibratile combs on the outer surface of the body, but by 

 the strokes against the water of the oral lappets or lobes. 



When the animal is resting, the oral lappets are widely extended at right 

 angles to the axis of the body (fig. 2). As movement begins, these lobes are 

 quickly raised from that position to one above the actinal pole, so that their 

 outer surfaces approach and almost touch each other over it (fig. 4). Both 

 lobes are then swung simultaneously downward, passing through an angle of 

 180°, and made to approach each other below the mouth, as in fig. 1. A 

 flapping motion of this kind is continued without interruption several times 

 and then ceases, the lappets returning to the position of rest with which they 

 started. When the inertia acquired by this flapping is lost, the motion is 

 again repeated. J Practically the "combs" contribute nothing to the motion 

 of the medusa. This larva, like the adult Ocyroe macula fa, has neither ten- 

 tacles nor tentacular sacs. The single specimen found was without doubt 

 immature, and we should expect to find a true tentacle hanging from its body 

 walls. In the young Bolina the tentacles are very large, while in the adult 

 they are reduced to simple club-shaped processes. In the Ocyroe larva there is 

 no indication of the tentacle nor of the tentacular sac. The adult also has 

 nothing which can be homologized to these structures.§ 



The body of the larva has a short axis, and resembles distantly that of a 

 young Bolina. The oral lappets are large, widely extended when at rest, and 

 crossed on their lower, inner surface by longitudinal muscles (fig. 5, /»;)-H 



* It may be the young of 0. maculata, 0. fusca, or 0. crystallina, as described 

 by Rang (Etablissement de la Famille des Beroides, Ocyroe, 1827). 



t Op. at., p. 294, PL IV. figs. 1-4. 



J A. Agassiz observed a Bimilar motion of the oral lappeta of 0. maculata, Bull. 

 Mus. Comp. Zobl, VIII. 7. 



§ This is true of the adult of 0. maculata. 



|| Tim study of these muscles in the young 0. eryttallvna leads me to believe that 

 I was wrong in considering the "spott" on the lobes of 0. maculata as mnscnlar la 

 character, an opinion expressed in a previous paper. (Bull. Mus, Comp. ZooL, 

 VIII. 7.) These snots in O. maculata are probably due to pigment in the walls of 

 the lobes. 



