566 DEVELOPMENT OF ECHINODERMATA AND ENTOZOA. 
anal orifice, tlieir larval zooids, like those of other Echino- 
derms, always possess both. It is from the side of the intes¬ 
tinal canal, that the young Echinoderm is usually budded-off. 
In some instances it separates itself completely from the 
zooid, when it has attained a certain stage of development, 
no part of the latter entering into its composition; this seems 
to be the case in the Gomatula , which present this further 
remarkable feature, that the young Echinoderm at first 
attaches itself to some fixed object by a footstalk (fig. 305), 
so as to resemble the fossil Encrinites in every essential 
particular, but afterwards becomes detached, and henceforth 
remains free (fig. 306). In the Starfish and Echinus , the only 
part of the larval zooid which is retained in the Echinoderm, 
is a portion that is (as it were) pinched-off from the stomach 
and intestines. In the Holothuria (fig. 67), on the other hand, 
which has a much closer conformity to the type of the Annelids, 
a much larger part of the larva is retained in the adult, and 
the process of development more nearly resembles an ordinary 
metamorphosis. 
742. Passing-on now to the Articulated series, we find 
that the developmental history of its lower forms presents 
phenomena not less remarkable than those already noticed. 
Eecent studies on the propagation of the Entozoa have re¬ 
moved many of the difficulties previously felt in regard to 
their mode of passage from one animal to another; by 
showing that the same creature may exist under two or more 
forms, which may differ so greatly from each other as appa¬ 
rently to belong to separate orders. This has now been 
ascertained to be the case, for example, in regard to the 
Tcenia or Tape-worm (fig. 53) and the Cysticercus (fig. 307). 
The segments of which the body of the Tape-worm is composed, 
are in reality repetitions (like the medusa-buds of a Hydroid 
zoophyte) of its generative apparatus; with this difference, 
however, that each segment contains both kinds of sexual 
organs, so that the eggs it contains are fertilized without any 
extraneous assistance. These segments, when mature, detach 
themselves one by one ; and being voided from the intestine, 
fall to the ground, over which the eggs they contain become 
disseminated by various agencies. Being swallowed with 
the herbage or the water ingested by herbivorous animals, 
the eggs are conveyed into their stomachs, viiere the little 
