56 MORPHOLOGY OF 



EXPLANATION OF PLATES I— VI, 



Illustrating Part I of Mr. Bateson's Memoir on the " Mor- 

 phology of the Enteropneusta." 



Complete List of Reference Letters. 



a. Amis. Ac. Archenteron. Al. Alimentary canal, a. I. Anal lappets, 

 ic.', ^ ^. The anterior, middle, and posterior body cavities respectively. The 

 letters / and r affixed to these letterings denote that the parts are of the left 

 or right side. br. Branchial chamber. C. Apical tuft of cilia. C. N. S. Cen- 

 tral nervous system, c. g. Groove between the collar and the trunk, cil. 

 Transverse band of cilia. Circ. Circular muscle-fibres. CI. Collar. CV . The 

 posterior fold of the collar, which eventually forms the operculum. Cl.sk. Skin 

 of collar. B. b. v. Dorsal blood vessel. D. mes. Dorsal mesentery. D. n. s. 

 Dorsal nervous system, dig. Digestive tract of alimentaiy canal. H. Ecto- 

 derm, ex. g. Refractive granules in mesoblastic cells. / Mesoblastic fibres. 

 q. s. Gill-slit. g. s. r. Branchial supporting rod. gl. Proboscis gland, gl. s. 

 Sac of proboscis gland, gn. Ganglion (?) cells. H. Hypoblast, ht. Heart. 

 Int. Intestine. /. r. Lateral rods of the skeleton, lu. Lumen of notociiord. 

 M' . M". M'". Mesoblast derived from the anterior, middle, and posterior pouches 

 respectively. Mo. Mouth, msc. Muscle-fibres, mu. Mucous gland, n. s. 

 Nervous system, n. oil. Neural canal. lie. pr. Pore by which the notochord 

 lumen opens into the pharynx. Nch. Notochord. N. pr. Neural pore. Op. 

 Operculum, p/ct. Fibrous substance of the nervous system. F. pr. Proboscis 

 pore. P. k. b. c. Perihsemal body cavity. P. sk. Skin of proboscis. Sep. 

 Septum between the horns of the anterior body cavity. Sh. Sheath of 

 notochord. Skr. Sucker. Sk. Skin. S. r. Supporting rod. Sp. Tissue-space 

 in the proboscis cavity, is. Testis. V. vs. Ventral vessel. V. n. s. Ven- 

 tral nervous system. Vlv. Valve of gill-slit. x. Pyriform cells of splanch- 

 nopleure of middle body cavity. 



With the exception of Figs. 5 and 6, the outlines were all drawn with 

 Zeiss's camera lucida. I have to thank Mr. Edwin Wilson of the Lithographic 

 Department of the Cambridge Scientific Instrument Company for drawing for 

 me two beautiful figures (Figs. 5 and 6) of the whole animal from preserved 

 specimens, and also for Figs. 1, 2, 3, and 4, which he has prepared for me 

 from my own sketches, the original outlines of which were traced from living 

 specimens. 



Fig. 1. — Whole animal seen from the side, immediately after the appearance 

 of the second pair of gill-slits. (Obj. A, oc. 2.) 



