MUSEUM OF COMPARATIVE ZOOLOGY. 293 



the growth preparatory to a fusion of the lobular tubes has gone still further, 

 so that the extremities of the lobular vessels almost touch each other. By far 

 the most important change has taken place in the lateral tubes, which are now 

 bifurcated at their extremities. 



The fusion of the lobular vessels appears in a larva (Fig. 5) following the 

 last. A junction of these tubes has here been effected, forming one continuous 

 vessel. In the same stage the auricular tubes have also pushed downward 

 through the bell walls, but they still end blindly and without division. They 

 also eventually fuse, and in a following stage (Fig. 6) they bend towards each 

 other and approach in such a way as to enclose the loop of the lobular vessels, 

 which has been already formed. 



In the next figure (6 a) the junction of the two auricular vessels has oc- 

 curred, so that a connecting loop is formed enclosing that already resulting from 

 a fusion of the lobular vessels. It will also be noticed that the lower ends of 

 the lateral tubes have bifurcated. Its terminal division (I I) is shown in the 

 foreground of the figure. At about this stage in the growth of the Ctenophore, 

 the lobes (ol), which later reach such a great size, begin to be differentiated 

 from the body of the medusa. In Fig. 7 they have pushed themselves still more 

 prominently into notice, and the network of lines upon their inner surface is 

 even now well marked. Meanwhile a slight variation in the direct meridional 

 course of the auricular tubes marks the situation of the future auricles (a). 

 The two branches formed by the bifurcations at the extremity of each lateral 

 tube have grown to such an extent that they join the auricular vessels one on 

 each side at a point directly below the position where the lower edge of the 

 auricles ends. 



The oldest larva of Mnemio'psis, which I have figured, shows nearly the same 

 disposition of vessels as one finds in the adult. Subsequent modifications in 

 the course of these vessels consist in their deviation from the direct meridional 

 lines, and their increase in length -, but no new junction of tubes takes place in 

 intermediate stages between this larva and the adult Mnemiopsis. 



DISCOPHORA. 



Dactylometra quinquecirra, A. Ag. 



Figs. 25-38, 38, 39. 



A single specimen of this interesting Discophore was taken by me in the 

 last summer, and from it a few new observations were made, which may add 

 something to our imperfect knowledge of its anatomy. 



The bell margin bears eight otocysts and a variable number of tentacles, 

 which have the following arrangement. If we take the interval of bell rim 

 between two otocysts we find appended to it a variable number of tentacles. 

 A figure is given of such a portion in which there are eight tentacles. Of 

 these the two tentacles adjacent the otocysts are larger than the remainder, and 



