MUSEUM OF COMPAKATR'E ZOOLOGY. 175 



are lined with a vibratile plate. There is a pair of auricular appendages in 

 each furrow, making four on both sides. 



The rudimentary tentacles are placed in a medial position in the furrow at 

 the extremities of a diameter passing through the longitudinal axis of the 

 mouth. They.are club-shaped (Plate VIII. figs. 7, 8, 9), and bear in their re- 

 duced condition small filaments or secondary appendages. These filaments are 

 also found on the adjacent ridges of the body, extending in two rows, one on 

 each side of the tentacle to the angle where the tubes from the " oral lappets " 

 and "auricular appendages " join (Fig. 10). The recess in which the rudimentary 

 tentacles lie is closed on one side by a " hood," d, Plate VIII. fig. 8. The tentacle 

 springs from the body walls, and is affixed by one end and by a part of the 

 lateral walls. In the adult the tentacle rarely projects beyond its socket. Its 

 secondary appendages, however, are often extruded beyond the rim of the hood 

 which shields the club-shaped tentacle to which they are affixed. The socket 

 in which the tentacle lies, and one wall of which is made by the " hood," is the 

 diminutive representative of the tentacular socket of Pleurobrachia. Scattered 

 pigment cells of crimson color in the base of the tentacle may represent a former 

 ocellus. On either side of the base of the tentacle, Plate VIII. fig. 7, 8, a, the 

 socket is continued into recesses not unlike the sense organs called " Riech- 

 griibschen " in the bell margin of Cyanea. 



The course of the lines of comblike swimming plates differs but little from 

 that of the same structures found on the surface of the body in other Cteno- 

 phorce. There are eight rows of combs, four of which are nmch longer than the 

 remainder. The modifications in their length are due to the abnormal develop- 

 ment of the oral lappets. The rows of vibratile combs, which are situated on 

 the same hemispheres from which the lappets are suspended, are much longer 

 than those which lie in the furrows between these lobes. Isolated single combs 

 from front and side are shown in Plate VIII. figs. 12, 12^ These combs retain 

 their power of motion even when separated from the jelly-fish, and are often 

 found rolled into a spherical ball, which is kept in rotation for a considerable 

 length of time by their combined motion. 



With the exception of eight small vessels passing along the upper surface of 

 the bell to the locomotive flappers, there are in Mnemiopsis no tubes which take 

 origin from the upper end of the " funnel " near the otocyst. All the tubes 

 arise from the lower extremity of the " funnel " just at its union with the upper 

 end of the stomach, and not from the other e.\tremity, upon which the otocyst 

 is situated. The " funnel " itself is very short, but is well marked. From the 

 lower end of the funnel arise six tubes, four of which by subsequent subdivision 

 form the tubes, which lie under the locomotive flappers, while the remaining 

 pair extend to the region of the mouth, each of the latter passing into a tenta- 

 cle, 6, Figs. 7, 8. The appearance of these tubes in the young Mnemiopsis, 

 when they closely resemble each other, is sho^vn in Fig. 8. 



The edge of the " auricular appendages " has fastened to it a vibratile plate, 

 which extends, without break, from the base on the side turned to the medial 

 line, to the angle which the rim of the oral lappets makes with the body of the 



