MICROIIYDRA DURING I907. I05 



faintly loni;;ihidinal lines that ultimately resulted in becoming 

 the radial canals. From 12.45 a. m. of May 18th, and per- 

 sistently thereafter, the innermost of the transverse lines men- 

 tioned gave convincing proof that it was to be the velum, 

 including the marginal canal and circular aperture ; and a 

 few minutes later every observer noticed more or less dis- 

 tinctly, upon the outer membrane or surface, radial lines 

 diverging from the apex or crown toward the position of the 

 marginal canal, adjoining the velum. From 2.15 a. m. the 

 approximately circular outline of the medusa changed to a 

 pear shape, widening, with nearly straight sides, from the 

 proximal to the distal end ; and the faint lines of the radial 

 canals became more marked. About 4.30 a. m. pulsation or 

 throbbing of the velum was observed ; at first a pair, one, 

 two; then, say a half minute later, one ; a pause, then, one, 

 two — one, two, and so on, ver>^ irregularly; and thus con- 

 tinued, perhaps increasing in force until 5.30, when the velum 

 with its aperture could easily be seen distended, pressing up 

 against and separating, at 6.20, the segmented tentacles as 

 shown in two excellent drawings by Miss C. W. Beekley, as 

 she saw them, parted, as when an orange is peeled from any 

 central point down to an equatorial line, and then forced 

 upward by internal pressure. 



I know not what other observers may have written as to 

 the formation of the earliest tentacles in marine medusa ; but 

 all our night watchers unhesitatingly agreed that my impres- 

 sions of ten years ago had been proved correct, in relation to 

 this species of fresh water forms. Of course, my theory 

 assumes that the wider portions of these wedge-shaped seg- 

 ments contract or, as it were, roll up upon themselves so as to 

 form the nearly cylindrical tentacles. I place great weight 

 upon the simultaneous appearance of the whole eight, with- 

 out the slightest suggestion of longitudinal growth. 



The throbbings of the velum continued irregularly after 

 the last drawing was made, finally liberating the medusa 

 about 9 a. m. of the same day (May iSth). Two days had 



