198 THE DOCTRINE OF DESCENT. 
body. We will not describe the highly complex transfor- 
mations of the larva here into an ophiura, there into a 
sea-urchin, and here again into a sea-cucumber ; but we 
will only inquire what can be the cause of this accord- 
ance in the earliest stages of individual development. 
There is no reasonable answer but the derivation of all 
echinoderms known to us from an older form, in the 
development of which our larva likewise appeared, and 
from which this common phase of development was 
transmitted to the whole family. But it is allowable to 
ask, further, how from a bilateral larva, one, that is, 
symmetric on two sides, should be evolved in animals 
of radiate structure, as are the greater number of mature 
echinoderms? 
On this point Haeckel instituted a conjecture which 
at first exasperated the systematizers of the old school, 
but which now gains more and more footing, and is sup- 
ported by the most recent comparative investigations, 
such as those of Hoffmann “On the Minute Anatomy 
of the Starfish” (“Ueber die feinere Anatomie der 
See-sterne”). The boat-shaped larva of the Echino- 
derms, especially a modification occurring in the star- 
fish, strikingly recembles a certain larval type of the 
marine Annelida. And asin the structure and distribu- 
tion of the parts of the rays of the echinoderms, espe- 
cially of the star-fish, an unmistakable. resemblance with 
the relative distribution and succession of parts of the 
Annelids is observable, Haeckel regards the Echinoderms 
as an offshoot of the Annelids. He considers that the 
oldest, and to us unknown, echinoderms originated as 
annelid stems ; the anterior end of the bilateral annu- 
lose parent-animal budding out gemmules in a radiate 
