244 Lieut. -Col. H. H. Godwin-Austen on new 
structures, such as muscles, elaeoblast, and probably also the 
genital organs. The distal portion of the left coelomic sac, 
which preserves the form of a tube, becomes the pericardium. 
This grows forwards, soon reaches the anterior portion of the 
germinal disk, and, becoming expanded like a club at its 
anterior end, assumes the shape which is already sufficiently 
well known from Kowalewsky’s description. The low r er wall 
of the expansion of the pericardial sac, which adjoins the 
endoderm, is differentiated tolerably early as a thickened 
plate, which represents the rudiment of the heart. The 
heart itself, which is formed by the invagination of this 
plate, is not completely developed until the period of the 
formation of the cyathozooid. 
With this I conclude these brief notes on the earliest stages 
in the development of Pyrosoma , and may summarize the 
chief results of my investigations as follows : — 
(i.) The embryo of Pyrosoma is formed from both fertilized 
and unfertilized elements, since not only the blastomeres, but 
also the kalymocytes, take part in the formation of the 
cyathozooid. 
(ii.) In the differentiation of the germinal layers the nuclear 
mass first divides into two portions — an ectoderm and a meso- 
endoderm ; of these the latter further differentiates into a 
multilaminar mesoderm and a unilaminar endoderm. 
(iii.) The mesoderm first appears in the form of two typical 
coelomic sacs. 
(iv.) Of the two coelomic sacs the left alone undergoes 
further development, and is subsequently differentiated into 
an axial mesoderm and a pericardial tube ; whereas the right 
sac breaks up into separate cells, which are afterwards dis- 
persed through the body of the cyathozooid. 
Odessa, March 1890. 
XXIX. — On supposed new Species of Land-Mollusca from 
Borneo belonging to the Genera Opisthostoma and Diplom- 
matina. By Lieut.-Col. H. H. Godwin-Austen, F.R.S., 
F.Z.S., &c. 
[Plate VII.] 
In the paper on Bornean Cyclostomacem published in the 
c Proceedings of the Zoological Society/ 1889, p. 332, 
I recorded and described all the species that were then 
known to me. Since that time I have received another small 
