MUSEUM OF COMPARATIVE ZOOLOGY. 115 
the blastopore, and the gastrula cavity or future intestine, as he confesses 
practically in a later paper.* 
The following quotation from Apostolides leads me to suspect that this 
author did not clearly distinguish the mesoblastic cells in his young Am- 
phiura with a single cavity (intestine) and single opening (anus), Possibly 
he confounded them with the hypoblast. He says:f “ Dans l’ectoderme 
on commence a4 apercevoir quelques points orangés premiers indices 
de calcification.” If these calcifications are really formed in the ecto- 
derm or epiblast, it is exceptional among larval Echinoderms, where they 
are regularly formed in the mesoblastic cells. Metschnikoff { rightly in- 
terprets the orange cells of the young Amphiura as mesoblastic or “cutis” 
cells. There is nothing in Apostolides’ account either of Ophiothrix or 
of Amphiura to show that he recognized these cells which play such an 
important part in the growth of certain parts of the larval Echinoderm. 
A study of Metschnikoff’s Fig. 6. Pl. III.{ is an instructive one. In 
this figure the epiblast (ep) is well formed, and the opening (an opening 
not figured, § but described in the text) on the lower pole is identified with 
the mouth opening of the older larve, which assume a bilaterally sym- 
metrical contour. The young Amphiura is already bilaterally symmetrical, 
for on each side of the “opening” can be seen the beginning of the 
vaso-peritoneal vesicles, or water-tubes (v). At the pole opposite the 
supposed mouth there are trifid bodies (cc), identified as the provisional 
spines of the pluteus. 
The homology of the parts of the larva mentioned has given me much 
trouble ; for if we regard the so-called mouth as the original opening or 
future anus, the positions of the water-tubes and spines as compared with 
the same stage in other Echinoderms are wrong. If the opening in ques- 
tion (mv) is a mouth or second infolding of the epiblast, where are the intes- 
tine and the anus? In his admission * that Apostolides is right in his 
interpretation of the homology of intestine and anus Metschnikoff must 
have abandoned the idea that the interpretation of this figure is a correct 
one so far as the opening mv is concerned. I have found a larva similar 
to the figure quoted (Fig. 6), with the two transparent bodies (v) which 
* Zeit. f. Wiss. Zobl., XXXVII. p. 307. 
+ Op. cit., p. 210. 
= Studien iiber die Entwickelung der Echinodermen und Nemertinen, Mém. 
de Acad. Imp. des Sci. de St. Pétersb., Vile sér. XIV. 8. 
§ There is a mistake in lettering and in description. On p. 15 mv is spoken of 
as mouth. mv in the explanation of Figs. 3, 4, 5, is the vitelline membrane (‘‘ Dot- 
terhaut”’). 
