TRANSACTIONS OF SECTION D. 837 
2. Phoronis, the Earliest Ancestor of the Vertebrata. 
By A. T. Masterman. 
The constitution of the group Chordata. The Hemichorda—Balanoglossus— 
Cephalodiscus, Rhabdopleura—The claims of Phoronis to be allied to the Hemi- 
chorda—Structural comparison of Phoronis to the Hemichorda (1) to Cephalodiscus, 
(2) to Balanoglossus—Absence of gill-slits and notochord—The ‘branchial fissure ” 
—Discovery of notochord in Actinotrocha—Structure and relations of notochord in 
Actinotrocha—Segments of the mesoblast in Actinotrocha—Relationship to 
Tornarta—Sugegested group ‘ Diplochorda’ and division of Chordate into Trimeta- 
mera and Polymetamera—Relationship to lower organisms (Echinodermata, &c.). 
3. The Effects of Pelagic Spawning Habit on the Life Histories of Fishes. 
By A. T. MAsterMan. 
The present position of work on Teleostean development—The ‘ontogenetic 
migration ’ as exemplified by plaice, herring, and sand-ee!—Method of investigation 
—Division of eggs into ‘pelagic’ and ‘demersal ’—Suggested ancestral character 
of pelagic eggs—Explanation of ontogenetic migration by phyletic migrations— 
Reasons for holding ‘ pelagic’ spawning habit to be ancestral—Effect of physical 
surroundings upon the pelagic stage—(1) Surface-currents (¢.g., plaice)—Displace- 
ment in two directions. (2) Change of salinity—Plaice of the Baltic—Fresh- 
water fish of pelagic descent—Flounder—Eel. (3) Temperature—Hastening of 
development and of ontogenetic migration—Fatality to fry—Plaice in Danish 
waters. (4) Change of life habit of fish—Change to demersal (littoral)—The 
‘ demersal ’ a specialised development—Littoral fish—Graphic representation of the 
life histores and solution of types from ‘pelagic’ type. 
4. The Structure of the Male Apus. By Dr. BenwaAm. 
5. On the Life History of the Haddock. 
By Prof. W. C. M‘Intosu, ID., F.R.S. 
