DEVELOPMENT OF ATRIAL CHAMBER OF AMPHIOXUS. 463 



EXPLANATION OF PLATES XXIX— XXXII, 



Illustrating Professor Lankester's and Mr. Willey's memoir 

 on the " Development of the Atrial Chamber of 

 Amphioxus." 



PLATE XXIX. 



Figs. 1 and 2. — Right and left surface-views of larva, with four gill-slits. 

 Length I'^QG mm. 



Fig. 3. — Head of latter, seen witli a deeper focus. Club-shaped gland 

 open to exterior only. 



Figs. 4 and 5. — Right and left surface-views of larva, with fourteen gill- 

 slits. Length 3"485 mm. 



N.B. — In Fig. 4 the reference line belonging to the words " edge of left 

 metapleur " has been carried too far, and touches the right metapleur. It 

 should stop at the ventral line of the larva. 



Fig. 6. — Head of latter, seen with a deeper focus. Club-shaped gland, 

 open at both lower and upper extremities, externally and internally respec- 

 tively. 



PLATES XXX, XXXI, and XXXII. 



The italics in Plates XXX, XXXI, and XXXII have the significance given 

 below, 



ant. at. Anterior opening of atrium, at. Atrium, at. p. Atriopore. 6r. e. 

 Modified intestinal epithelium bordering the gill-slits. d. a. Dorsal artery. 

 d. I. m. Double-layered membrane, separating myocoel from splanchnocoel. 

 d. m. Dorsal division of myoccel in connection with dorsal fin. d. ic. Dorsal 

 wall of atrium, ext. a. External aperture of club-shaped gland, g. s. Gill- 

 slit. Int. Intestine. Int. a. Internal aperture of club-shaped gland, ^-d. 

 Club-shaped gland. I. a. Left dorsal artery (unpaired). /. m. Lower lip of 

 mouth. /. met. Left metapleur. m. Mouth, m. e. Modified epithelium on 

 wall of mouth-cavity. mus. Muscle-plates. my. Primary myoccel. my'. 

 Secondary upgrowth of myocoel, between the muscle-plates and notochord and 

 nerve-cord. n. c. Nerve-cord. 7ich. Notochord. neph, Nephridium of 

 Hatschek. neph. a. Opening of so-called nephridium into mouth-cavity. 

 0. h. Commencing oral hood. r. d. Right embryonic diverticulum from the 

 intestine, r. c. So-called " renal " cells of W. Miiller. r. met. Right meta- 



