438 FERNANDUS PAYNE. 



the only method of distinguishing the two ends of the young 

 hydroid (Figs. 7, 8, and 9). Shortly after the formation of the 

 solid endodermal mass of cells, the whole structure begins to 

 change shape. Elongation begins at the animal pole (Fig. 7). 

 This produces a larva somewhat pointed at one end and large at 

 the other. About this same time a cavity begins to form in the 

 endodermal cells (Fig. 7). Presumably this is formed by migra- 

 tion and rearrangement of cells. Elongation continues and along 

 with it the cavity in the endoderm enlarges (Fig. 8). At the 

 end of these processes the larva is practically uniform in diameter 

 from end to end and has a single layer of endodermal cells 

 surrounding a central gastrovascular cavity (Fig. 9). The one 

 distinguishing mark is the unequal size of the ectodermal cells 

 at the two ends. Which of these stages is the typical planula is 

 difficult to say. Dalyell's planula was elongated and ciliated, 

 and the endoderm was still a solid mass. In Craspedacusta the 

 cilia are lost and the endoderm is formed before elongation 

 begins. The gastrovascular cavity is formed during elongation. 

 This elongated larva or planula attaches at one end and grows 

 into the typical hydroid. A description of the hydroid need not 

 be given as this was done in my former paper (Payne, '24). 



This completes the life history of this interesting form, which 

 for several years has made sporadic appearances here and there, 

 only to disappear without revealing to us much of its story. 



SEX. 



In all earlier finds of Craspedacusta, with the exception of 

 those in Boss Lake, the medusae were reported to be males. In 

 Boss Lake all medusae were females. Why were both sexes not 

 found together? In my former paper I answered this question 

 by suggesting that possibly the environment might be a de- 

 termining factor; also that the hydroids might be male or 

 female producing. It was my inclination to favor the latter 

 interpretation. The fact that we now find both males and 

 females in the same environment would also favor such an 

 interpretation. The sexes are approximately equal in number in 

 the Kentucky River, a count of 110 giving 52 females and 58 

 males. They are also equal in size in so far as I can judge with 



