188 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Horse-Leech in Man.* — Dr. M. C. Francaviglia describes a case in 
which Hirudo sanguisuga occurred with serious, though not fatal, results 
as a temporary parasite on the nasal mucous membrane of a contadino 
who had presumably satisfied his thirst incautiously. Other cases of the 
parasitism of Hirudinea in man are noted. 
j8. Nemathelminthes. 
Mermis nigrescens.f — Dr. v. Linstow describes this nematode 
whose larvae are very common in Orthoptera near town, though not in 
those of the open high-lying country. The sexual forms hide in the 
earth, in summer after heavy rains they ascend plants. Development 
occurs in the uterus, the ripe ova contain fully developed embryos and 
are laid in the earth. Thence the larvae enter Orthoptera. The author 
describes the anatomy and histology of the parasite. Suffice it to say 
that Mermis resembles Gordius and Nectonema in its ventral (as well as 
dorsal) nerve-strand, and Ascaris in the connection between the nerve- 
strand aud the muscles ; that like Nectonema it has a narrow, thick- 
walled, chitinous (esophagus and no anus, that it further resembles 
Ascaris in the position of the female genital aperture, and in the presence 
of two cirri and papillae on the tail-end of the male. In the absence of 
an anus, it agrees not merely with Nectonema , but with Ichthyonema , 
Dracunculus, Allantonema , Atractonema, Aprocta, and other Filariae. 
Sub-cuticular Layer of Ascarids.J — M. L. Jammes describes the 
development by the young Ascaris of a cuticular layer which protects it 
from the action of the digestive juices in the midst of which it lives. 
He points out that this cuticle exerts a direct influence on the organism 
which it protects, for it causes an arrest in the development of the 
primitive cellular ectoderm. In thus early suppressing most of the 
external relations it makes any division of labour extremely difficult. 
The anatomical differentiations which distinguish the nervous system 
from the rest of the ectoderm do not appear. 
The largest number of cells is found in the cephalic region and 
around the canal and seminal orifices ; in the intermediate regions the 
cells degenerate and form fibrils. It is in this retrograde development 
that we have to seek for the cause of the variations observed in the 
number and position of the cells of the granular layer. At first they 
form a continuous stratum, but soon, many of them having no cause to 
exist because of the presence of the cuticle, diminish in number ; they 
persist chiefly in the parts which correspond to the first rudiment of the 
nervous system. 
The observations of Marion lead to a belief in the existence, in 
Nematodes, of a uniform nervous substance, distributed around the 
animal, and the author believes that he has been able to demonstrate the 
existence of this substance in Ascaris. 
M. Jammes is of opinion that the nervous system described by 
authors and the granular layer, are formed by one and the same tissue, 
the basis of which are the neuro-epithelial elements. These last are 
* Bull. Soc. Rom. Stud. Zool., i. (1892) pp. 233-41. 
+ Arch. f. Mikr. Anat., xl. (1892) pp. 498-512 (2 pis.). 
X Ann. Sci. Nat., xiii. (1892) pp. 321-42 (1 pi.). 
