MUSEUM OF COMPARATIVE ZOOLOGY, 181 



3. Eows OF 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 or 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 Chsetosoma 

 (Giard et Barrois, '75), there is found a double row of hairs along a 

 portion of the ventral line. The setae 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. Muscular 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 



