LUCERNARI^ AND THEIR ALLIES. 



Id 



will become evident upon consulting the figure (fig. 122, B), which we shall use 

 to illustrate the next step; we will merely state here that 2 begins to develop 

 before 2^, although in the same row. The -f- on the right of the diagram indicates 

 where the next tentacle is to appear in tlie fourth row, and serves to set out the 

 one-sidedness of the group, and its thread of development, in a stronger light. 

 150 (A). In other groups (.A>. 121, B, B\ B-, B\ 122, B) on the same indi- 



vidual, there are five tentacles in four rows, the youngest of which is numbered 4, 

 and the four others as in the previous group (A). It will be noticed, perhaps, 

 that the succession of numbers is not alike, in point of position, in each bunch, 

 for instance, in one group the numbers 1, 2, 4 lie on the left, as the observer faces 

 the anterior end of the body, and in another bunch, 1, 2, 4 are on the right. Now, 

 if the vertical plane of the body be assumed as a dividing line, we shall have 

 these numbers in the two uppermost groups standing as if in antagonism to each 

 other, the line of development in one trending in the opposite direction from that 

 in the other ; and so it is in the two lower groups ; and likewise on the two sides 

 of the horizontal plane. Or, if we look at them from another point of view, 

 making the partitions (i^') the dividing lines between the two groups nearest to 

 them, Ave shall find the same antagonism, but with a reversal of th(> trtuid, so that 

 1, 2, 4 in each bunch lie next the partition. This gives us the clue to the one- 

 sidedness of the groups, the preponderance, as we have noticed in the early part 

 (§ 12) of this memoir, being on the side next the partition; for after the first 

 tentacle was assigned its place, the second appeared on the side nearest the parti- 

 tion, and thenceforth threw the balance of age and size in that direction. 



150 (B). Before any member of the fifth row begins to develop, anotlier tentacle 

 of the fourth row appears on the side most distant from the partition. It is 

 numbered 4'' (_fi(js. 121, C, C, 122, C). Thus far we have been 

 dealing with the tentacles of one individual, and have found some 

 slight variation in the number of these organs in different groups, 

 but yet always preserving, in the order of their succession, a 

 perfect symmetry relative to the partition. Their further develop- 

 ment will be illustrated in the next section (§ 21). 

 151. The size of the largest tentacles in these young gropj)* is much greater, 

 in proportion to the magnitude of the body, than at maturity, as they measure 

 in length from one-sixth to one-fourth the diameter of the umbella, i. e., an average 

 of one-fifth, but are very thick and stout, the diameter being at least one-fifth as 

 great as the length. In the adult the proportion is as one is to twenty-five. As 

 for the globose tip, it is (piite distinct, but not remarkably prominent, and is about 



