140 BULLETIN OF THE 
careous bodies (fig. 100, op. cit. pp. 67, 68) to the “ Basalplatte,” of the 
so-called ‘ Stiihlchen,” in the skin of the Holothurians, and to the “ Rid- 
chen” of the Chirodote. He considers that the ‘“ Chirodotaridchen 
den Basualplatten der Seesternstachel gleichzusetzen sind, gewissermas- 
sen rudimentire Stachel darstellen, bei denen sich die ganze Ausbildung 
auf die Entwicklung einer Basalplatte reducirt hat.” 
A. Agassiz has called my attention to the resemblance of similar 
bodies in Echinarachnius to the calcareous wheels in the Holothurians. 
It seems probable that the stellate bodies in the young Echinarachnius 
are the same as the “ Basalplatte” of the spine of Asterina.* It was not 
observed that these bodies, as they first appear in Echinarachnius, bear 
a definite relation either to the ambulacral tubes or the intermediate 
intervals which we may suppose are the interambulacral regions. Al- 
though a large number of plutei were examined, the number of these 
bodies was not found to be uniform. Some plutei have five, some 
one, others three, and many more than five, of these trifid calcareous 
bodies. As the echinus grows older the ends of the three spurs of the 
trifid spicule became divided or bifurcated, and even subdivided, while 
in some cases these bodies were again subdivided. In all these cases 
they are still enclosed in a transparent cyst or cell, similar to that 
figured by Metschnikoff for the “ Hohlkehlen.” This sheath or capsule 
is supposed to be the outer enveloping layer, epiblast, of the spine. It 
was of course my first impression that these rods were the beginnings 
either of ocular or genital plates, and I turned to A. Agassiz’s memoir 
on the development of the starfish, where similar calcareous bodies are 
found, to see if it were not possible to homologize them with the plates 
which first appear in the Asteroidea. It was not possible to satisfac- 
torily compare these structures, and I was then led to inquire whether 
these structures are the beginnings of plates or of other parts of the 
echinoid body. My observations at present have not gone far enough 
to answer these questions satisfactorily. If these trifid bodies are the 
beginnings of plates it cannot be stated at present whether they are 
ocular or genital plates, and there is a doubt in my mind whether they 
are plates of the test or spines of the same. 
Pl. VII. fig. 16, is an instructive stage in the development of the sea- 
urchin within the body of the pluteus. On the right-hand side of the 
figure we see the ambulacral feet, am, of which there are more than 
five, the additional having probably formed by lateral budding. On 
* Compare fig. 10, p. 69 (Ludwig op. cit.) with the trifid bodies of Echinarach- 
nius. See also fig. 100, op. cit., a, b,c. 
