PLATE 111 
A 
Fin. I. — Successive stages in the segmentation of Sycandra raphanus. 
( Copied from F. E, Schulze f 
A. Stage with eight segments still arranged in pairs, seen from above. 
B. Side view of stage with eight segments. 
C. Side view of stage with sixteen segments. 
D. Side view of stage with forty-eight segments. 
E. View from above of stage with forty-eight segments. 
F. Side view of embryo in the blastosphere stage, eight of the granular 
cells which give rise to the ectoderm of the adult are present at 
tlie lower pole. 
cs. Segmentation cavity ; ec. granular cells, which form the ectoderm ; 
en, clear cells which form the endoderm. 
Fig, 2 . — Larva of Sycandr,^ raphanus at pseudogastrula stage, in situ in the 
maternal tissues. Copied from F. E. Schulze), 
me. Mesoderm of adult ; hy. collared cells, or endoderm, of adult ; en. clear 
cells of larva, which eventually become involuted to form the endoderm^ ; 
ec. granular cells >of larva, which give rise to the ectoderm ; at this 
stage they are part ially involuted. 
Fig. 3. — Two free stages in the development of Sycandra raphanus. 
( Copied from F. E. Schulze). 
A, Amplisblastula stage. 
B, A later stage, after the ciliated cells have commenced to become 
invaginated. 
cs. Segmetation cavity ; ec. granular cells which form the ectoderm ; 
en. ciliated cells, which become invaginated to forSi the 
endoderm. 
FIG.4 — Fixed gastrula stage of Sycandra raphanus 
( Copied from Schulze). 
The figure shews the amoeboid ectoderm cells {ec) 
derived from the granular cells of the earlier stage, 
and the columnar endoderm cells, lining the gas- 
trula cavity, derived from the ciliated cells of the 
earlier stage ; the larva is fixed by the amoeboid 
cells on the side on which the original mouth 
opening is situated. 
'IG. 5. The young of Sycandra raphanus, shortly after the development of 
the spicules ( Copied from Schulze). 
L. View from the side. 
1 . View from the free extremity. r -i- , 1 Thp 
r. Osculum ; ec. ectoderm ; en. endoderm, composed of ciliated cells. 1 ne 
terminal osculum and lateral pores are represented as oval — 
spaces. i 
The author is indebted ^ the kindness of F. M. Balfour, Esq,, F.R.S.f for the loan of the Plate, s, from which the Fi gures are produc ed. 
