96 



LOWER INVERTEBRATES. 



Fig. 89. — Scyphistoma of Aurelia flavidula. 



Discophora. It was then called Scyphistoma or Scyphostoma, and, notwithstanding 

 we now recognize that it is part of the life history of the young of another genus, 



it is convenient to retain the name as char- 

 acteristic of the first of the attached larvae 

 of these animals. 



The Scyphistoma larva of Aurelia, for 

 the following larva has not been observed 

 in our Cyanea, although there is no doubt 

 that its development is identical with that 

 of Aurelia, is followed by one called the 

 Strobila, which like the former is still 

 attached to some fixed object. In the 

 growth of the Scyphistoma, that part of the free end of the larva situated inside the 

 circle of tentacles, and in which the mouth lies, gradually rises higher and higher, 

 forming an elongated cylinder of great relative size as compared with that of the 

 original body of the Scyphistoma, which lies at its base, and ujDon which it is borne. 

 There next forms on the outer wall of this cylinder a number of parallel constrictions 

 which encircle the body of the cylinder in waving lines. These constrictions become 

 deeper as the larva gets older, imparting to it a remote likeness, as Professor Agassiz 

 has pointed out, to a "pile of saucers" resting below on the 

 remnant of the Scyphistoma body and increasing gradually 

 in size from the lowest member to the saucer which caps the 

 pile. The next change in the progress of the development of 

 Aurelia, after the Strobila just mentioned, is one in which 

 the attached condition is abandoned and a free locomotor 

 larva again adopted. This condition, for a reason identical 

 with that mentioned with regard to the Scyphistoma, may 

 be called the Ephyra, and more closely approaches tliat 

 assumed by the adult than any of the others. Tlie whole 

 fixed Strobila, however, does not break" from its attachment 

 and swim away as an Ephyra, but fragments of the same, or 

 individual saucers which compose the pile, in consecutive order one by one drop from 

 their attachment and swim away as perfect little EphyriE. The cycle is now complete, 

 and although the Ephyra differs greatly in form from the adult, yet still there are few 

 important additions, and no departure from a direct growth in passing from one into 

 the other. 



By reviewing the history which has just been considered it will be seen that in 

 two of the intermediate larval conditions, known technically as the Scyphistoma and 

 Strobila, between the egg and the parent, we have a wide departure from the adult in 

 mode of life as well ns external shape. We have seen also that the ScyjDhistoma does 

 not pass directly as a whole into the Ephyra, but that it divides into fragments, each 

 of which becomes a perfect adult. From one Strobila a number of Ephyras are 

 produced without any conjugation of sexes in the attached animal. From this latter fact 

 the mode of reproduction is said to be asexual and the Strobila an asexual individual. 

 Gathering together the whole history of the development into one chain we find 

 it presents this remarkable circumstance. Between the egg and the female Discophore 

 from which it came there is an asexual, sessile larva which multiplies in an asexual 

 way by simple division, thus pi-oducing from one egg a numerous progeny, each of which 



Fig. 90. — Strobilia of Aurelia 

 Jkividula. 



