322 
I’KOF. E. W. MACBKIDE. 
24. Vernon. — “ The Relations between the Hybrid and Parent Forms 
of Echinoid Larv®,” ‘ Pliil. Trans. Roy. Soc. (Lond.).' series B. 
vol. cxc, 1898. 
25. “Cross-fertilisation amongst Echinoids,” ‘Arch. Ent. niech.,' 
vol. ix, 1900. 
. EXPLANATION OF PLATES 14 and 15, 
Illustrating' Prof. E. W. MacBride’s paper entitled “ Studies 
on the Development of Echinoidea, Part II.’^ 
List of Abbreviations Employed. 
ab. Skeleton of aboral spike of Echinocardium larva, ad. Adoral 
ciliated band. a. 1. Skeleton of antero-lateral arm of larva, an. Anns. 
h. r. Body-rod of skeleton of larva, calc. First rudiment of skeleton of 
larva, cil. Anterior tuft of long cilia and posterior tuft of long cilia 
in Echinocardium larva, cce. Coelomic sac. cr. In-bent crook of body- 
rod in skeleton of larva of hybrid and of Echinus, dil. Dilator muscles 
of coelomic sac. f. Fertilisation membrane, li.r. Horizontal rod of 
larval skeleton, int. Intestine, l.p.c. Left posterior ccelom. mad. 
Normal left madreporic pore, mad.' Right madreporic pore of Echino- 
cardium lai’va. mes. Primary mesenchyme, oes. (Esophagus, p. d. 
Rudiment of skeleton of postei'o-doi'sal arm. pr. o. Rudiment of iira*- 
oral arm. p.o. Skeleton of post-oral arm. r.p>.c. Right posterior 
ccelom. st. Stomach, siom. Stomodueum. 
[All the figures were drawn from living larvae with the help of the 
camera lucida, and all the larvae figured are represented with a uniform 
magnification of 200 diameters so that their relative sizes can be seen.] 
PLATE 14. 
Fig. 1. — Egg of Echinus esculentus treated with the sperm of 
Echinocardium cor datum and examined twenty-four hours after- 
wards. f. Fertilisation membrane. 
Fig. 2. — Blastula of Echinus esculentus twenty hours old. 
Primary mesenchyme in the act of being formed. 
Fig. 3. — Late gastrula of Echinus esculentus two and a half 
