304 W. K. BROOKS ON THE LIFE-HISTORY 



our species, and the planula undoubtedly becomes directly converted into the larva 

 shown in fig. ]. 



The larva next makes its way into the bell cavity where it fastens itself by the 

 tips of the tentacles, as shown in PI. 44, fig-. 6. Its proboscis now becomes enormously 

 lengthened, as shown in PI. 44, fig. 1, and its enlarged tip is inserted into the mouth of 

 the Turritopsis, while two new tentacles are developed between the first two, and soon 

 become equal to them in length, and the aboral end of the body becomes a little elon- 

 gated, between the bases of the tentacles, as shown in fig. 1. 



The interesting fact that the larva shown in PI. 44, fig. 1, is a true hydra, differing 

 from the actinula larva of Tubularia only in the length of its proboscis and the small 

 number of tentacles, has been almost completely overlooked by all recent writers, al- 

 though it did not escape McCrady's attention. He says in his second paper, in his 

 diagnosis of the genus Cunina (48, p. 108), "Larva a free hydra, like the free stage 

 of the Tubularia," and on p. 12 of his first paper (49), "The resemblance of these 

 beings to the free young hydra of Tubularia was unmistakable." Very soon after the 

 larva fastens itself by its tentacles, and either before or soon after the two secondary 

 tentacles are developed, it begins to multiply asexually by budding from the aboral 

 process between the bases of the tentacles, and thus forms little communities, like the 

 one shown in PI. 43, fig. 2, which is copied from McCrady, who calls attention on p. 21, 

 to the obvious fact that this method of budding from an area which is aboral to the 

 tentacles is directly comparable with what occurs in the fixed hydroids, when this part 

 of the body becomes the stem or root. On p. 14, he states his belief that no more than 

 two buds are ever developed at one time, but this is an error, as communities like the 

 one shown in fig. 3, consisting of six or seven larva?, are frequently met with. This 

 figure will also serve to illustrate the changes through which the larva passes during 

 its development and conversion into the medusa. The young buds have, at first, no 

 tentacles and no mouth, but the proboscis soon lengthens, the mouth appears at its tip, 

 and two opposite tentacles grow out from its base, and are soon followed by two more, 

 alternating with, and at first shorter than the primary tentacles. A rim or flange now 

 grows out from the wall of the body, and in the zone which is occupied by the bases of 

 the tentacles. This zone which is to become the umbrella of the medusa occupies the 

 same position as the inter-tentacular web of such hydroids as the Campanopsis- 

 larva of Eutima, although, unlike the inter-tentacular web, it is composed of both layers 

 of the body wall, and contains a circular diverticulum from the digestive cavity. Four 

 more tentacles now make their appearance, alternating with the first four, and the cir- 

 cular lim becomes notched or infolded opposite the base of each tentacle, or more 

 strictly the fma edge between the tentacles grows faster than it does elsewhere, and thus 

 converts the rim into eight marginal lobes, each of which contains a pocket or diver- 

 ticulum from the central digestive cavity. The tentacles are at first on the rim, in the 

 notches between the lobes, hut they verv soon begin their migration towards the aboral 

 pole of the body. It is important to note that the lobes are at first directly comparable 

 to the marginal lobes of an Ephyra, inasmuch as their free edges are entirely separated 

 from each other. As the tentacles retreat however, and the notches deepen, the endo- 

 derm alone is infolded, thus leaving the bottom of each notch spanned over by a double 



