180 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
while one forms the oesophagus, the other gives rise to the stomach and 
rectum. On the fusion of the blind ends of these two pockets a con- 
tinuous tube is formed. The central nervous system arises as a shallow 
pit in the floor of the atrium ; this pit becomes closed over by a fold of 
the inner layer only of the polypide, which thus forms a sac, the walls 
of which become the ganglion. The kamptoderm (Kraepelin), or 
funicular sheath of Allman and Nitsche, is formed by the conversion of 
the columnar epithelium of the two layers of the wall of the atrium into 
pavement epithelium. The funiculus arises from amoeboid cells derived 
from the coelomic epithelium. The wall of the colony grows by cell- 
proliferation at its margin. 
The budding of Cristatella presents conditions transitional between 
direct and stoloniferous budding ; this genus differs from Alcyonella in 
that the tip of the branch grows independently of the polypides. Each 
of the layers of the younger bud arises from a part of the same cell mass 
as that which gave rise to the corresponding layer of the next older bud. 
The digestive epithelium and the nervous tissue are both derived from 
one and the same layer of cells, the inner layer of the bud. The 
alimentary tract of a young Cristatella is similar to that of a young 
endoproctous Bryozoon. The author does not agree with Harmer in 
saying that the ganglion of the Phylactoloemata arises exactly as in the 
Endoprocta. 
The circumoral region of the ring canal of Cristatella is in free com- 
munication with the ccenocoel in all stages of development, and is not, 
as Kraepelin maintains, closed. The two arms of the lophophore arise 
independently of each other. The ancestral Bryozoon probably pos- 
sessed a U-shaped row of tentacles which encircled the mouth in front, 
and ended freely behind. The tentacles near the mouth are, phylo- 
genetically, the oldest. The epistome arises as a fold continuous with 
the wall of the oesophagus below and the floor of the atrium above, and 
it communicates with the coenocoel by means of the epistomial canal. 
The migration of the funiculus is probably assisted by amoeboid cells. 
The origins of the retractor and rotator muscles migrate along the radial 
partitions from roof to sole ; the separation of the two muscles is 
secondary and due to the separation of their points of insertion. The 
disintegration of the neck of the polypide is begun by a metamorphosis 
of the protoplasm of its cells ; the metamorphosed cells break away and 
leave the atrial opening. That part of the body which lies round the 
atrial opening arises by proliferation of cells derived from the neck of 
the polypide. The ectodermal cells become metamorphosed by an 
intercellular secretion of small gelatinous balls which fuse ; the contents 
of more than one cell often fuse into a single large mass. 
Arthropoda. 
a. Insecta. 
Ontogeny of Insects.* — Dr. E. Urech has made a physical and 
chemical analysis of the urine of a large number of species of Butterflies, 
and has discovered a close relation between its pigments and those which 
colour the wings of Lepidoptera in general. The first urine is alone 
* Arch. Sci. Phys. et Nat , xxiv. (1890) p. 52G. 
