256 



F"ig. 3. Echinuplulcus Iransrcrsiis, sjji'cies f. Nenlral view. 'I'lic vibralilc l)aiul iiol (Jisliiicl 

 over the Eeliinoid-rudinicnt. *'/,. 



4. Same larv^ as lij,'. 'A, in ilorsal vii'w. *'/,. 



5. Youiifi larva of Mcllila se.virsiitr/orata (Leske); 21 hours old. Ventral view, ""/i- 

 fi. Larva of sanu- species, same age; side view. ""/,. 



Plate XIV. 



Kig. 1. Young larva of I.acianuin diplopora H.L.Clark: 'A days old. N'ciilral \ iew. ^""/i. 



2. Hnihryo of (^lypeasler japoitlciis Dodcrl.. 2',, days old. Showing hegiiuilng forma- 

 tion of the skeleton, '""'i. 



I{. Larva of same species, 11 liays old. Ventral view. Drawn from life. '"/i. 



4. Gastrula of Echiiiarachnius mirabilis (A. Ag.), 18 hours old. '*"/,. 



."). Fully developed larva of Eclunarachnius (Dcndrasler) excentricus (Escli.). 11 days 

 old. Ventral view. From a preserved specimen, condiincd wllli ;i sketch from a 

 living specimen. Skeleton dissolved, '"'^/i. 



6. Larva of same species, same age; side view. Slightly restored, '"^/i. 



7. Larva of F.nropv micropora Ag., II days old; ventral view. From a preserved spec- 

 imen, combined with a sketch from a living specimen, ""/i- 



Plate XV. 



All figures of I'croiiclla Lcsiicuri (Val.). Figs. 1 — 1 drawn from life, ''/i! the rest '""/i- 

 Fig. 1. iMnbryo, five hours old. in the hlastula-stage; showing irregular folding of the ecto- 

 derm. 



2. Young larva. 17 hours old. The moulli has hccii formed, and the })osloral arms 

 are beginning lo ap|)ear as a pair of small lateral thickenings. 



3. Young larva. 20 hours old; dorsal view. The postoral arms are distinct. 



4. Fully formed larva, .'ii) hours old; ventral view. The preoral lobe has been completely 

 reduced, the mouth opening now being at the anterior edge of the body. 



5. Longitudinal section of an endiryo, 9 hours old. .\ number of mesenchyme cells 

 have been formed, but gastrulalion has not yet begun. 



6. Longitudinal section of an emliryo, 12 hours old. Gastrulalion lias begun. 



7 — 10. From a series of longitudinal sections of an embryo, 16 hours old; showing 

 the shape of the entoderm. Between figs. 7 and 8 there is one section, fig. 9 following 

 immediately after 8; there arc 3 sections between figs. 9 and 10. 



- 11 — 13. From another series of longitudinal sections of an embryo, 16 hours old; showing 



the shape of the entoderm. Fig. 11 is the more dorsal of the three. In fig. 13 is seen 

 the apical Ihickening. 



- 14. Longitudinal, sagittal section of an embryo, 16 hours old. I'lie nuiutli (ni) has begun 



lo form. 



- 1.5 — 18. From a series of frontal, longitudinal sections of an embryo, 18 — 20 hours old. 



Fig. 1."), which is the more dorsal of them, shows llie widening (am.) from the lower 

 end of llie pharynx (ph.), surrounding the entoderm (ent.); this widening gradually 

 disappears in the following figures. In fig. 18 is seen the rectum (r) in a lateral posi- 

 tion. There are 4 sections between figs. 1.') and 16, 1 between figs. 16 and 17 and 

 4 sections between figs. 17 and 18. 



- 19 — 22. From a series of sagittal longitudinal sections of an embryo, 18 — 20 hours old. 



Showing the posterior prolongation (am.) from the pharynx (ph.). .Mso the shape 

 of the archenteron (ent.) appears from a comparison of these figures. Fig. 20 shows 

 the blastoporus, which has now shifted to the ventral side, to form the anal open- 

 ing (a). 



Plate XVI. 



.Ml figures of I'eroncUa Lcsucuri (\'al.); all ""/i. 

 Fig. 1. Longitudinal, frontal section of a larva 23-24 hours old. Showing the amniotic 

 prolongation (am.) of the pharynx (ph.) continuing to the posterior end of the body. 

 The pari in the middle is the raised ventral wall of the amnion (comp. figs. 1 1 16); 



