MUSEUM OF COMPARATIVE ZOOLOGY. 181 
3. Rows or Hairs. 
The lateral rows of hairs are evidently developed in connection 
with the free life of Nectonema. Moreover, they are not structures 
without a parallel among the Nematodes. Many forms have been de- 
scribed with hairs distributed irregularly cr regularly — sometimes in 
rows (Trichoderma) —over the surface of the body. Unfortunately, 
in such cases little or no idea has been given of the size and struc- 
ture of the “hairs” by the authors who have mentioned them. In 
one form at least, the peculiar free-living marine genus Chetosoma 
(Giard et Barrois,’75), there is found a double row of hairs along a 
portion of the ventral line. The sete are hollow and entirely super- 
ficial, thus agreeing in several points with those of Nectonema ; they are 
not, however, so extended in their distribution as in the latter form. 
4, Muscutar LAYER. 
The complete degeneration of the posterior portion of the alimentary 
canal in the adult, as well as its minute size in comparison with the body 
of the worm, makes it at once evident that this organ cannot be func- 
tional in the adult. The question then suggests itself as to the source 
of nourishment during this period of life. As has been already noted, 
the protoplasmic zone of the muscular layer is thicker in the immature 
individual, and diminishes in thickness with the attainment of sexual 
maturity. This decrease in volume may take place in two ways, — by 
the formation of corpuscles directly from the cells of the layer, and by 
the giving up of food matter to neighboring cells or to the coelomic fluid 
and thus to all tissues of the body. 
As has been shown, the corpuscles of the body cavity probably originate 
from the cells of this layer by a process of abstriction. This process is 
never very extensive, so far as I have been able to judge, and hence will 
hardly serve to explain entirely the decrease in the volume of the layer. 
One is, therefore, compelled to accept the second method suggested, that 
of the indirect transmission of food matter either through neighboring 
cells to remote tissues, or by means of the fluid in the body cavity. The 
unusually large size of the protoplasmic portion of the muscle cells, and 
its granular condition, are well explained on the supposition that these 
cells have secondarily acquired the function of storing up nourishment 
for the support of the body during the period of adult life. 
VOL. XXIII. — NO. 3. 13 
