292 BULLETIN OF THE 



The successive stages in the growth of the young Mnemiopsis are as follows. 



In the youngest larva which was taken we recognize most of the organs of 

 the adult. The lateral tubes (/), which originate as simple blind sacs, end 

 in the neighborhood of the lips without bifurcation. The eight remaining 

 vessels, situated meridionally just below the surface beneath the rows of 

 " combs," resemble each other in size and have about the same length, each 

 also ending blindly in the body walls.* Fig. 1 represents this larva, drawn in 

 a plane passing through the tentacles and the otocj^st. The two auricular 

 vessels (a t) are seen to lie adjacent to the tentacles, one on either side, while 

 the lobular tubes Q t) are situated in the segments between them. 



A clearer conception of the relationship of the chymiferous tubes to each 

 other may be obtained by a consultation of the following figure (1 a), taken 

 from the actinal pole. In no other way can the origin of the chymiferous 

 vessels from the funnel be shown to such advantage as by a drawing made in 

 this way. The eight meridional tubes spring in pairs from a vessel (c) which 

 arises from the base of the funnel (/). From the point of bifurcation also, 

 there originates a tentacular tube (i t), which passes to the tentacular sac. 

 This tube exists in the youngest larva studied, as a very broad vessel, and in 

 subsequent growth it becomes more and more slender and tubelike, as shown 

 in following figures. The lateral tubes (/) originate independently of all the 

 others, as short diverticula from the base of the funnel. 



Fig. 2 represents, in the same plane as the above, a larval Mnemiopsis some- 

 what older than the last. The most marked difference between the vessels of 

 the two is produced by a growth of the lobular vessels, which have lengthened 

 more than the auricular, and now extend about half-way down the length of 

 the body. In other respects they are unchanged. The latei-al tubes {I) have 

 remained in about the same condition as in the previous stage, and have not 

 yet bifurcated at their extremities. 



In Fig. 3 the lobular vessels are represented as having extended still farther 

 in their growth, and are rapidly approaching the oral pole of the medusa. 

 Their extremities have even turned towards each other preparatory to a final 

 union. The auricular tubes have also lengthened and pushed their way about 

 two thirds the whole distance from the apical to the oral pole. 



Fig. 4 represents a larva somewhat more developed than the last, in which 



* In my descriptions tlie lobular vessels correspond witli wliat Mr. Agassiz calls 

 the "long ambulacral tubes (longitudinal ambulacra)," and the auricular vessels 

 with his " short ambulacral tubes (lateral ambulacra)." The adjectives lobular and 

 auricular seem to me preferable to "long " and " short," to avoid confusion in a com- 

 parative study of these structures in other Ctenophores (contrast the long and short 

 ambulacra of Cestus and Ocyroe). I have abandoned the adjective "lateral," as ap- 

 plied to ambulacra, in order to avoid confusion with other vessels (7) designated by 

 the same name, on each side of the stomach. Between the older term " longitudinal " 

 and the new adjective lobular, I have chosen the latter, as more characteristic. The 

 nomenclature adopted seems to me to call attention to characteristic features in all 

 genera of Chao-phora., as well as of Mnemiopsis. 



