1108 General Notes. [ November, 
a spherical gastrula, large circular blastopore, later the body is 
elongated, the blastopore closes completely, a ring of strong cilia 
forms about the blastoporic area, the blastopore being placed 
eccentrically in the ring. The body becomes constricted by a 
transverse ring, a second forms behind it, and the body is thus 
cut off into three regions corresponding with the future proboscis, 
collar and body portion; the end of the proboscis is furnished 
with a tuft of cilia. -A groove forms in the middle line of the 
dorsal region of the collar, and at the same time the dorsal nerve 
cord is delaminated from this ectoderm. At the same time a pore 
perforates the skin behind the collar on either side, placing the 
endoderm and the ectoderm in communication, and furnished 
with cilia, it is the first pair of gill slits. The mouth forms in 
front of the collar at the base of the proboscis, and later the anus 
arises at the opposite end of the body. In the species whose life- 
history is dealt with in this paper, viz., Balanoglossus kowalevskit, 
the development in the external form proceeds by the direct 
growth from the form now arrived at to the adult by the elonga- 
tion of the body, the addition of the gill slits and the differentia- 
tion of the body region into the branchial and digestive portions, 
and the disappearance of the ring of cilia and the tuft of cilia 
upon the proboscis. There is thus no Tornaria stage included in 
the life-history of B. kowalevckit, but the development is direct. 
Bateson does not discuss the question of the relations between 
the echinoderms and Balanoglossus, reserving it for the fuller 
discussion that is promised in a future paper. 
The history of the internal changes is briefly as follows: The 
endoderm was invaginated, as seen from the surface; from it arises 
the mesoblast in three separate masses, one anterior unpaired 
mass in the proboscis, two anterior lateral masses, two posterior 
lateral masses. These all arise as diverticula of the archenteron, 
and their cavity, at first continuous with that of the primitive gut, 
! 1es the various portions of the body cavity. A forward pro- 
liferation on the dorsal side of the gut wall, with at first an open- 
ing into the gut cavity, gives rise to a solid supporting organ 
which runs from the collar region into the proboscis, and is the 
homologue of the notochord of the Chordata. The walls of the 
