42 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
these animals, and, on comparing them, sees a distinct resemblance 
between them. In both, the musculature consists of plate-like structures 
set in regular series ; in one there is a central space filled by sarco- 
plasm, and of the value of a muscle-cell, and in the other it appears to 
be solid and surrounded by sarcoplasm. In both a number of the mus- 
cular columns that form the plates have the character of motor-fibres 
and pass transversely inwards to a sharply circumscribed cord, which 
extends to the nervous system. In both Amphioxus and Mermis the 
motor-fibres of either side do not arise simultaneously, but a certain 
distance behind one another to the right and left of the nervous system ; 
in Mermis , however, there is not the same regular metamerism as in 
Amphioxus. In both the motor-fibres are accompanied by sarcoplasm 
which, in Mermis , distinctly forms the element that admits of innerva- 
tion, while in Amphioxus it probably is, but cannot be with certainty 
asserted to be so. 
Holomyaria.* — Dr. E. Rohde asks a question, which has been asked 
before, Are there any holomyarian Nematodes ? Schneider, when form- 
ing the group, took Gordius as its chief representative, but Grenacher and 
Biitschli have contended that the musculature of that worm is formed of 
cells of the ccelomyarian type seen in Ascaris. Dr. Rohde does not deny 
that such coelomyarian cells exist, but there are, he says, in G. tolosanus 
others of quite a different structure. They differ from the others in that 
they are completely open, not only on the inner, but also on the outer 
margin, and they are, consequently, formed essentially of two parallel 
plates, which are connected by the central medullary substance. Fur- 
ther, in the coelomyarian cell the contractile margin extends as far as the 
inner boundary of the musculature, where there is but little medullary 
substance ; in the others the plates extend hardly further than the middle 
of the muscular layer, but have on their inner side a well-developed 
medullary substance, in which numerous nuclei are contained. 
These two kinds of cells are not only found together, but at their 
boundaries pass gradually into one another. Between the cells of both 
types there are olten thin band-like masses of protoplasm, which have 
exactly the same appearance as the medullary substance of the cells. 
There can be no doubt that we have here to do with the first develop- 
mental stages of the muscle-cells, and it further seems clear to the author 
that the cells of the second type are cells in a young stage. 
The histogenesis of the muscle-cell of Gordius would appear, therefore, 
to be this. The young cell consisting only of protoplasm, and probably 
connected with the subcuticle, as is the case in many cells of Ascaris (see 
above), commences its further development by becoming differentiated 
into muscular columns on the part which is turned towards the sub- 
cuticle. These columns become arranged in plates, gradually reach the 
inner boundary of the muscular layer, till at last the cell is cut off from 
the subcuticle, while at the same time the primitive protoplasm becomes 
almost completely used up. The development of the muscle-cell may 
go still further, for in some the contractile margin grows together on the 
inner side, and then, as in all Hirudinea, encloses the medullary sub- 
stance. 
Gordius preslii presents quite a different structure of the musculature 
♦ SB. K. Akad. Berlin, 1892, pp. 665-7. 
