( 455 ) 
SUMMARY 
OF CURRENT RESEARCHES RELATING TO 
ZOOLOGY AND BOTANY 
( 'principally Invertebrata and Cryptogamia ), 
MICROSCOPY, &o., 
INCLUDING ORIGINAL COMMUNICATIONS FROM FELLOWS AND OTHERS* 
ZOOLOGY. 
A. VERTEBRATA Embryology, Histology, and General. 
a. Emtoryologry.f 
Theory of Germinal Layers and the Parablast.ij: — M. F. Houssay, 
who lias been investigating the formation of the circulatory system of 
the Axolotl, calls attention to a comparison that it is possible to institute 
between the different products of the ectoderm and endoderm. 
I Epiblast 
Neuroblast 
Plus three contacts with 
Endodermj 
1. The mesoblast; canal of the pronephros. 
2. The parablast : lateral blood-vessel. 
3. The metablast; openings of the branchial 
clefts. 
| Mesoblast with an axial portion Notochord. 
Parablast Subnotochord. 
Metachord 
(rudimentary). 
| Parablast 
Protohypoblast < .(Metablast .. 
lDeutohypobla 3 t| Hypoblast _ 
The metablast appears to the author to be characteristic, more than 
any other peculiarity, of Vertebrates (inclusive of Balanoglossus ). The 
first stage of the parablast is segmented ; it arises from the proto- 
hypoblast by plates. 
M. Houssay completely rejects the mesoderm as indicating a third 
layer. Comparably to the ectoderm and endoderm, it has no more 
value than the parablast, metablast, or neuroblast. If, he says, you 
speak of three layers, why not of six ? He enunciates the general law 
that the point of origin of all the systems of organs of even complicated 
* The Society are not intended to be denoted by the editorial “ we,” and they do 
not hold themselves responsible for the views of the authors of the papers noted, 
nor for any claim to novelty or otherwise made by them. The object of this part of 
the Journal is to present a summary of the papers as actually published , and to 
describe and illustrate Instruments, Apparatus, &c., which are either new or have 
not been previously described in this country. 
f This section includes not only papers relating to Embryology properly so called, 
but also those dealing with Evolution, Development, and Reproduction, and allied 
subjects. 
X Comptes Rendus, cxiv. (1892) pp. 1128-30. 
