﻿Dec, 1856.] 



ELLIOTT SOCIETY. 



75 



shall, therefore, speak hereafter of the region of the proboscis and 

 about the mouth as the lower parts of the larva and the tentacula 

 and gemmiparous area as upper parts. 



Just beneath the circle of tentacula then, at this period, we 

 observe an incipient bulging from the surface of the hydroid, 

 which extends around the whole digestive bulb. This may be 

 seen at fig. 26, g, PI. 6, and was also observable in a still more 

 rudimentary degree in the smallest of the three feeding larvae 

 already referred to, PI. 5, fig. 28b. This bulging fold now be- 

 comes conspicuous, and about the same time a new tentacular 

 knob begins to be visible in the interspace between each pair of 

 tentacula, as represented in the figures last referred to, where, 

 however, their appearance seems to be rather earlier than usual. 

 The appearance of these tentacula, nevertheless, may be con- 

 sidered as nearly synchronous with that of the bulging fold. Im- 

 mediately after this, eight points, at equal distances from each 

 other, appear, from the somewhat hanging or overlapping border of 

 the fold. (PI. 6, fig. 27, t, t.) These points elongate somewhat, 

 and may now be discovered to contain each two otolithic chrystals 

 placed one below the other, the lowermost being always the larger 

 of the two. (PI. 4, fig. 28a, a much magnified outline.) These 

 are otolithic cysts, but I have never observed the chrystals to 

 vibrate. There are now eight distinct tentacula, the four new ones 

 having become somewhat more elongated and distinct as seen PI. 

 6, fig. 28. Each of the otolithic cysts corresponds in position to 

 the interspace between two tentacula. Shortly the border of the 

 fold between the auditory cysts assumes a more specialized ap- 

 pearance resembling a cord around the margin. At the same time 

 the gemmiparous area of the larva becomes more rounded and 

 protuberent, assuming gradually the form of the upper surface of 

 a free Medusa. The larva at this stage is represented PI. 6, fig. 

 28. The disk is now so far developed, the growing fold so far 

 overbrows the sides of the body that it is seen to be capable of 

 contraction and dilatation exactly in the manner of the pulmograde 

 movements of Discophoras, yet not in the rapid rythmical succes- 

 sion which distinguishes those perfect forms, but very slowly, so 

 that several, perhaps many minutes may elapse between a single 

 contraction and the following expansion, and indeed these move- 

 ments at this time do not seem to have any co-ordination or ryth- 

 mical relation between their successive acts. That phasis does not 

 appear until later. Synchronous with those movements, however, 



