Fewkes.] 
102 
[Dec. 5, 
thought to show the close likeness of the young of Asterias and 
Asterina. If we should consider the aboral side of the body we 
should notice other resemblances. The terminal is cap-like in both, 
and in both Asterias and Asterina shields the last formed ambula- 
cral rafters as represented for Asterina in fig. 1. 
Evidently thus far in the growth of the two genera there is per- 
fect accord as far as the oral plates are concerned and we may con- 
clude that pentagonal and stellate asteroids arise from a starfish 
with these characters. 1 Prior to this stage there is nothing to in- 
dicate that one is to have a pentagonal, the other a stellate form. 
On the aboral side we find another common feature in these two 
genera. We find in both the medial row of dorsals formed in the 
same sequence and with the same prominence. In both genera this 
prominence is lost in later stages, but in early forms they are iden- 
tical. Moreover, we notice that dorso-lateral plates of the arms 
begin in the same way, but soon they lose their resemblance, one 
genus passing into a pentagonal, the other into a brachiated aste- 
roid. 
The adambulacrals, ad, of the arm of Asterina form between 2 the 
marginal ends of the ambulacrals as in Asterias. They follow the 
same law in the time of formation and those nearest the mouth are 
developed first. They originate in pairs, while the ambulacrals are 
well formed before the intermediate adambulacrals appear. 
It would be interesting to turn to the origin of these plates in 
these typical genera in order to discover how far back in the his- 
tory of these starfishes this difference, if any, extends, and to note 
any variation in growth of the two forms. It would seem as if em- 
bryology ought to throw considerable light on this basis of classi- 
fication. Are these plates in the mouth parts of Asterina formed 
in a different way from the plates of an Asterias, or are the compo- 
nents of the circle of mouth plates simply the same, only differently 
modified in each case? 
I believe that in both genera they are the same, and that the 
same plates in one instance assume the form of adambulacrals, 
1 In order to determine the sequence of plates in another pentagonal starfish, I un* 
dertook the study of the development of Palmipes, but was unsuccessful. I was able, 
however, to observe a novel fact in regard to the ova of this genus. A mature female 
Palmipes laid strings of yellow eggs in my glasses. I am not familiar with any Echi- 
noderm which drops the ova in strings as in this genus. Ova were deposited at Roscoff 
in August. 
2 While this is their primary position, it becomes ultimately, however, more or less 
lost, and as in Asterias in the adult it is almost impossible to make out. 
