AN UNDESCRIBED ACRANIATE. 245 



EXPLANATION OF PLATES. 



All the figures are reduced from camera lucida drawings of 

 Asymmetron lucayanwn. 



PLATE XIII. 



Figure 1. Right side of an adult having 45 . 8 . 14 = 67 myo- 

 tomes ; reduced to J- the diameter of the original drawing from the 

 living specimen. 



Figure 2. Left side of the same specimen ; from a drawing 

 made a day later than the above. 



Figure 3. Left side of a preserved immature specimen having 

 43 . 8 . 15 = 66 myotomes and 27 gill-slits. The small ventral 

 caecum is shown at c. 



Figure 4. Left side of an opaque, preserved specimen 14 mm. 

 long, having 44 . 8 . 13 = 63 myotomes, gill-slits from the 10th to 

 35th myotomes and' 28 gonads extending from the 16th to the 43d 

 myotomes. The lines a-h indicate the regions of the transverse 

 sections shown in Figs. 11-15 and 21-23 of Plate 2. 



Figure 5. Left side of one of the youngest larvae. A preserved 

 specimen 6 ram. long with 22 gill-slits and 51 . 13 = 64 myotomes. 

 The caecum is not yet formed. 



Figure 6. Ventral view of anterior region : from an immature 

 preserved specimen having the pre-oral hood expanded. 



Figure 7. Transverse section of brain cut 12 //, posterior to 

 its anterior tip; showing the pigment bordering this end of the 

 ventricle. 



Figure 8. A section of the same series 40 //, posterior to the tip 

 of the brain, where the ventricle is at its widest. 



Figure 9. From the same series, 52 /JL posterior to tip, where 

 the ventricle is coming rapidly to a close. 



Figure 10. Left side of the anterior extremity of a mature 

 specimen macerated in Haller's liquid. The relative positions of 

 lymph spaces and canals are shown. The dotted line is the anterior 

 limit of the muscle fibers of the first myotome. 

 3 



