OF THE ACALEPHiE OF NORTH AMERICA. 293 



tubes are entirely destitute of either eje-specks or tentacles, these being altogetlicr 

 limited to the junction of the radiating tubes with the circular tube. In Tiaropsis, how- 

 ever, the tentacles and eye-specks are not only uniformly distributed along the whole mar- 

 gin without any prominent tentacle or eye-speck at the junction of the tubes, but between 

 the tubes there are, all round, two larger eye-specks, making altogether eight, arranged 

 at equal distances in the intervals between the radiating tubes. This peculiarity is the 

 more striking, as in most of the naked-eyed Medusae the development of eye-specks 

 seems to be prominently connected with the vertical chymiferous tubes and the margi- 

 nal tentacles ; while here the eye-specks are decidedly a morphological modification of 

 the marginal appendages, being homologous to the tentacles with a simple eye-speck 

 at their base, with which they are placed in one row and upon one level, differin;^ in 

 the degree and intensity of development, assuming a much more independent position, 

 and leading almost to the peculiar arrangement characteristic of the common large 

 Steganophthalmic Medusae. The tentacles are not hollow, and no chyme is circulated 

 in their interior in a more special manner than must take place everywhere in the 

 process of assimilation. But here the chyme, as such, is not circulated in particular 

 ramifications of the circular tube beyond the margin of the disk, while in Sarsia it 

 penetrates into the four marginal tentacles. The tentacles all round the margin of 

 the disk are of nearly uniform length, and of uniform size and thickness ; though, upon 

 close examination, sufficient differences may be perceived between them to satisfy us 

 that their number is constantly increased by the additional development of new ones 

 between the older (Fig. 13). This is especially striking upon comparison of very young 

 specimens of Tiaropsis with more advanced ones, the number of tentacles being 

 hardly one fourth of what it is at a later period, or, as the development is rather 

 uniform in these animals, and almost all sj/ecimens caught at ihe same time are 

 nearly equally developed, the comparison has to be made from recollection and mem- 

 oranda of earlier states of growth contrasted with mature specimens, when it becomes 

 plain that the eight large eye-specks, with few intervening tentacles, are developed very 

 early (Fig. 14), and numbers of tentacles, with rudimentary eye-specks, are successively 

 formed in the intervening spaces of the older ones (Fig. 15) ; but the larger prominent 

 ocelli (Fig. 16), while they undergo their gradual development, remain unchanged in num- 

 ber, there being but eight of them throughout life. Their position, also, is rather singular : 

 they are all at equal distances from each other (Plate VI. Fig. 5) ; but, with reference to 

 the radiating tubes, they are placed so that one radiating tube meets the circular tube e.\actly 

 midway between two eye-specks, thus dividing the continuous track of the circular tube ex- 

 tending between two such eye-specks into two equal parts, while between the next eye- 



40 



