THE EMBRYOLOGY OF A SCORPION. 137 



that the changed conditions of development^ due to terrestrial 

 life, and the consequent pressure on the embryo, may have pro- 

 duced this change. A detailed account of the development of 

 these appendages in Limulus may throw more light on the 

 matter, but, unfortunately, though many authors have attacked 

 the problem, a complete and satisfactory account of the develop- 

 ment of Limulus is not yet in existence. 



EXPLANATION OF PLATES XIII, XIV, XV, XVI, 

 XVII, & XVIII, 



Illustrating Mr. Malcolm Laurie's paper on '^The Em- 

 bryology of a Scorpion (Euscorpius italicus)." 



Abbreviations. 



a. c. Air-cavity in gill-book, ac . Air-spaces between the lamellae of gill- 

 book, ab. ap. Abdominal appendage, am. Amnion, am. c. Amniotic cavity. 

 ap. Appendage, bl. Blastoderm, bl. s. Blood-space, bl. c. Blood-corpuscle. 

 cau. Caudal segment, ce. Cerebral ganglion, ce. in. Cerebral invagination. 

 ceph. Cephalic segment, cce. Coelom. cox, Coxal gland, cox. d. Duct of 

 coxal gland, ep. Epiblast. ep'. Extension of epiblast beyond ventral plate. 

 fol. Follicle, fol'. Outer non-cellular layer of follicle, g. I. Ganglion of 

 clieliceral somite, ger. Germinal epithelium or inner layer of ovarian tube. 

 ger'. Yolk-forming cells derived from germinal epithelium, ge. t. Genital 

 tube. hi. Heart. hy. Hypoblast. /;/. Extension of hypoblast beyond 

 ventral plate, hy, m. Mass of hypoblast in caudal segment, int. Intestine. 

 /. Gastric gland, mes. Mesoblast. mi. Prolongation of ovarian tube to egg. 

 mlph. Malphigian tubes, n. g. Neural groove. n. n'. Nucleus, nucleolus. 

 n. c. Nerve-cord. n. gl. Nerve-ganglion. n. th. Neural thickening, oc. 

 Central eye. oc'. Lateral eye. o. I. Outer layer of ovarian tube. ov. Ovum. 

 p. gl. Poison-gland, pr. hy. Primitive hypoblast (hypomesoblast). proct. 

 Proctodseum. pr. t. Primitive thickening, rtn. Retina of central eye. 

 rtt^. Third layer of central eye, post-retinal membrane, s. m. Serous mem- 

 brane, s. m! . " Peripheral cells." som. mes. Somatic mesoblast. spl. mes. 

 Splanchnic mesoblast. st. Stomodseum. ste. p. Steruocoxal process, stg. 



VOL. XXXr, PART II. NEW SER. K 



