436 MORGAN. [Vol. V. 



dorsal pore, a pair of collar pouches with exceedingly small 

 openings into the archenteron, and a posterior pair of folds 

 with larger openings into the archenteron. These evaginations 

 subsequently pinch off and form the body cavities. The ner- 

 vous system forms in the mid-dorsal collar region by delamina- 

 tion of ectoderm, and at its two ends it increases by invaginations. 

 The details of the later stages need not be given here. The 

 upper anterior fold of the digestive tract is continued forward 

 under the proboscis gland with the base of the proboscis, and 

 Bateson speaks of this as the notochord, and believes it to be 

 homologous with the same organ in the Vertebrates. A single 

 pair of gill slits first appears, and others form behind it seriatim. 

 The tongue bar develops in them. The collar pores are formed 

 by hollow invaginations of ectoderm opening into the body 

 cavity of the collar, and are to be compared to the brown funnels 

 of Amphioxus. The so-called heart (proboscis vesicle) is formed 

 from an accumulation of mesenchymatous tissue. Bateson's 

 statement that the cavity of the sac of the proboscis gland opens 

 anteriorly into the enteroccel, is an error, I believe. Its origin 

 from a closed vesicle in Tornaria points to this, and I have ex- 

 amined carefully the adult of B. Kowalevski and found no open- 

 ing. Bateson does not decide whether Tornaria or the larva of 

 B. Kowalevski represents the more primitive form of develop- 

 ment. He minimizes the supposed relationship of Tornaria to 

 the Echinoderm larva, and appears not to believe in the rela- 

 tionship to the Echinoderms. On the other hand, he draws 

 attention for the first time to the relationship of Balanoglossus 

 to the Vertebrates. The following similarities of organs in 

 the two forms point to this relationship : i, the notochord ; 

 2, the gills, branchial skeleton, and blood supply ; 3, the cen- 

 tral nervous system ; 4, the origin of the mesoblast ; 5, the 

 peculiar fate and remarkable assymmetry of the anterior pouch ; 

 6, the atria (or folds of the collar) ; 7, the excretory funnels. 

 There followed a speculative portion on the ancestry of the 

 Chordata. 



Spengel published in 1884, after Bateson's first contribution, 

 an abstract of his work on the anatomy and embryology of 

 Balanoglossus. He showed that in B. Knpfferi there is a right 

 and left water pore (I may state here that in a single individual 

 of B. Kozvalevski I found a pair — right and left — of water 



