or THE NEMATOIDS, PAEASITIC AND FEEE, 561 



by Walter, the results of my own researches are mostly in accordance with them, and 

 Ebertii* has also testified to their correctness. 



Speaking generally, the longitudinal muscles may be said to be composed of a series 

 of small muscle-cells varying in form between an elongated spindle and a rhomboidal 

 shape, each of which is composed of one portion (cortical) altered in structure by its 

 conversion into fibrillae, and another less altered portion varying in its proportional 

 extent, containing in the midst of the granular medullary substance of which it is com- 

 posed one or more nucleated cells, and often sending off a transverse prolongation to, or 

 in the direction of, one of the median lines. In their most divei'gent types two well- 

 marked differences exist in the nature of these muscle-cells in different species of Nema- 

 toids, though intermediate states may be seen, which clearly point out these varieties to 

 be nothing more than modifications of one common plan. This distinction was first 

 noted by Dr. Schneider, and he proposes to divide the Nematoids into Platymyarice and 

 ColomyaricB, according as they agree most with one or other of these types of muscle- 

 formation. As illustrations of the first type, we have the Spirojjterce, Strongyli, and 

 Oxyurides, whilst the second is seen to perfection in the members of the genus Ascaris. 



Beginning with the simpler forms, the Platymyarice, we may take the Spiroptera obtusa 

 as a good illustration. In this animal the muscle-cells are flat, and of a somewhat 

 elongated rhomboidal formf, accurately dovetailing in with one another so as to form 

 four continuous layers separated from one another by the longitudinal lines;};. On the 

 surface they have a gi-anular aspect, and present a nucleated cell generally near the 

 centre imbedded in this granular material. By the aid of thin transverse sections of 

 the animal we obtain a much clearer insight as to the precise structure of each muscle- 

 cell §, and are enabled at once to see that each is composed of an external solid contrac- 

 tile portion, and an internal granular matter bounded by a loosely fibrous envelope 

 (Plate XXVI. fig. 21). We shall speak more fully of these various parts after having 

 described their modifications met with in animals of the other type. 



The structure of the muscles in the Colomyarice may be well studied in any of the 

 Ascarides, and in none better than in A. lumbricoides and A. megalocephala, where the 

 type attains its greatest complexity. Whilst in Spiroptera obtusa the breadth of each 

 muscle-cell at its widest part considerably exceeded its depth or thickness, in these ani- 

 mals, on the contrary, the depth considerably exceeds the breadth, and they exist as 

 triangular cells with a more or less elongated base (Plate XXIII. figs. 8 & 9), by which 

 they are attached to the deep integumental layer, whilst their other sides and apices, from 



* Untersuch. uber Nemat. 1863, p. 64. t Untersuch. uber Nemat. Taf. ix. 3. 



X ScHNEiDEB has pointed out what he considers to be the general arrangement of these muscle-cells in the 

 Platymyari(K, after what he has more especially observed in Oxyuris curvula. (Eeich. and Du Bois-Eeym. 

 Archiv, 1863.) 



§ There is a great apparent difference in the size and breadth of contiguous cells, simply owing to the section 

 having passed through these in most cases at varying distances from their central or broadest part — a section 

 which passes through nearly the centre of one cell may intersect the narrow extremity only of the npxt. 



MDCCCLXVI. 4 I 



