250 
K. M. SMITH AND H. G. NEWTH. 
divide the splanclmocoel from another cavity external to it 
is the parietal wall of the coelom, which in the process of 
preservation has become separated from the ectoderm. 
The facts elucidated by Messrs. Smith and Newth enable 
us to compare the collar cavity of Ampliioxus directly with 
the mandibular cavity of the embryos of Petromyzon and the 
Elasmobranch embryo. This cavity has been observed by 
Hatta to originate in Petromyzon from the wall of the gut 
independently of the outgrowth which gives rise to the 
myotomes behind, but in both Petromyzon and the Elasmo- 
branch embryo the mandibular cavity becomes subsequently 
connected by a long tongue-like ventral extension with the 
splanclmocoel. 
List of Woeks Referred to in this Paper. 
1. MacBride, E. W. — ‘’ The Early Development of Ampliioxus,” ‘ Quart* 
Journ. Micr. Sci.,’ vol. xl, 1898. 
2. “ Further Remarks on the Development of Ampliioxus.” 
‘ Quart. Journ. Micr. Sci.,’ vol. xliii, 1900. 
3 . “ The Formation of the Layers in Ampliioxus and its Bearing 
on the Interpretation of the Early Ontogenetic Processes in 
Other Vertebrates,” ‘Quart. Journ. Micr. Sci.,’ vol. liv, 1909. 
4. Lankester, E. Ray, and Willey, A. — “ The Development of the Atrial 
Chamber of Amphioxus,” ‘ Quart. Journ. Micr. Sci.,’ vol. xxxi, 
1890. 
5. Wijhe, J. W. van. — “ Beitr. z. Anat. des Kopfregion des Amphioxus 
lanceolatus,” ‘Petrus Camper,’ vol. i. 1901. 
6. Goodrich, Edwin S. — “ On the Structure of the Excretory Organs of 
Amphioxus,” ‘ Quart.. Journ. Micr. Sci.,’ vol. liv, 1909. 
EXPLANATION OF PLATE 18, 
Illustrating Messrs. K. M. Smith and H. G. NewtlTs paper, 
“ A Note concerning the Collar Cavities of the Larval 
Amphioxus.” 
Abbreviations. 
The asterisk marks the communication between the left collar somite 
and the gut. 
