608 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
On the whole, the development of the germinal layers in Phoronis 
recalls that which one is in the habit of finding in the Trochophora- 
type ; the presence of more than two primitive mesoblast-cells is a sign 
of inferiority, and suggests that their presence in the Trochozoa is a 
simplification of a primitive plurality such as is found in the larv£B 
of some Platyhelminths. 
j 8. Nemathelminth.es. 
Histology of Ascaris.* — M. L. Jammes states that he has searched 
in vain, in Ascaris megalocepliala , A . lumbricoides and A. suilla for the 
epithelial layer formed of very small cells which Leuckart thinks lies 
against the muscle-cells. The so-called granular layer has been found 
to be continuous, and identical in structure, with the oesophageal nerve- 
ring ; both are formed of fibrils mingled with cells. Sections taken 
along the body show, in this granular layer, small beds of cells which 
are often arranged in several rows, but never form a continuous epithe- 
lium. These cells arc rarely cubical, sometimes rounded, often flattened 
parallel to the wall of the body, and have a varying number of pro- 
longations. No intercellular substance was ever found. 
The great resemblance in structure between the granular layer and 
the nervous system allows us to suppose that the former represents the 
ectoderm ; this would differ much from the ectoderm of other Metazoa, 
in being formed of neuro-epithelial elements. If this be so the nervous 
system described by various authors would be merely a condensation of 
this layer in different parts of the body. The author is testing this 
hypothesis by embryological researches. 
y. Platyhelminthes. 
Anatomy and Histology of Nemertines. t — Hr. O. Burger has 
given considerable attention to the structure and systematic relations of 
the Nemertinea. They all have a ciliated cylindrical epithelium which 
either contains the whole of the glandular mass of the skin, in which 
cases it rests upon an almost structureless layer of connective tissue, or 
some of the gland-cells sink into the layer of connective-tissue, where a 
cutis is formed, which is often rich in muscles. The appearance of this 
cutis leads to some considerable changes — the appearance of an external 
layer of longitudinal muscles, of subepithelial muscular layers, and the 
formation of a muscular tissue at the cephalic extremity. The Enopla 
are characterized by a cephalic gland. In all groups there is found the 
radial musculature, the bands of which divide into chambers the muscular 
layers of the dermo-muscular tube. By the presence of a ciliated 
epithelium and numerous gland-cells, the integument of the Nemertines 
exhibits a distinct resemblance to that of the Turbellaria. The Annelids 
as a rule have no cutis, but such a layer has been described by Andrew 
in Sipunculus nudus. In both Annelids and Nemertines the naked 
gland-cells of the skin become greatly swollen at the time of sexual 
maturity, and the dermo-muscular tube of Annelids resembles that of 
many Nemertines in that it consists of a circular and a, longitudinal 
* Comptes Reudus, cxi. (1890) pp. 65-6. 
f Zeitsehr. f. Wiss. Zoul., li. (1890) pp. 1-277 (10 pis.). 
