RADIATA. 31 
expelled when the animal wishes to sink. It is probable that this may be 
accomplished to a certain extent by the muscular power of the air-vessel. 
Blainville thinks that this order (which wants the radiated character), with 
Beroe and Diphyes, may be allied to the Mollusca, and in the year 1836 he 
proposed for them the name JMalactinozoaria, under the impression that 
they constitute an intermediate division. 
Orver 6. SysrorigrapA. The name Diphyida is derived from that of the 
genus Diphyes, in allusion to its double nature, each animal being composed 
of two somewhat conical pieces, the point of one being inserted a short 
distance into the larger end of the other, and retained by a very slight 
attachment. See the Penny Cyclopedia for an extended account, illustrated 
with figures of this and the preceding orders. 
Sars, a distinguished naturalist of Norway, discovered in 1836 that some 
of the Acalephe resemble the Zoophyta, in having a gemmiparous 
reproduction. He observed certain projections from the base of the pedicle 
(or exterior of the stomach), which proved to be budding young, attached 
by the upper or outside portion of their disk. These young resemble the 
adult in all essential particulars, and, like the 
Hydra, they have an independent action 
previous to their separation from the parent. 
This is represented at a, in the annexed figure 
of Lizva octopunctata of Sars (an animal about | 
one fourth of an inch long), as given by Forbes. | 
The species is named from the eight black | 
ocelli, four of which are large, and towards | 
these the gastric vessels are directed. In 
Sarsia prolifera, Forbes, the gemmation 
takes place at the base of the exterior 
tentacles. i | | 
We come now to describe a mode of generation which has no parallel in 
the higher animal forms, and to which the Meduse and some other animals 
are subject. This mode is termed <Alternation of generations by the 
Danish naturalist, Steenstrup, who has the credit of generalizing the facts 
upon which the theory is founded, and of which he is in part the discoverer. 
An English translation of his work on the subject, by George Busk, was 
published by the Ray Society in 1845, entitled, “On the Alternation of 
Generations; or the Propagation and Development of Animals through 
Alternate Generations : a peculiar form of fostering the young in the lower 
classes of animals.” Besides this author, the chief observers in this curious 
branch of science are Chamisso, who published observations on the Salpz 
in 1819; Sars, on the Meduse, between 1828 and 1841; Siebold and 
Lovén in 1837; and Van Beneden in 1844-7. (See the Cyclop. of Anat. 
and Phys., Art. Polypifera.) | 
This phenomenon is described by Steenstrup as that of “an animal 
producing an offspring, which at no time resembles its parent, but which, 
235 
