CUTICLE AND MOULTING (8.8.435)133 



resolve the striae into components ; occasionally, however, they are resolv- 

 able into rows of excessively fine dot-like elements, as for instance in 

 bathybius, reversus and incurvus. Lateral wings to the cuticle are almost 

 unknown, and the striae are not perceptibly altered on the lateral fields; 

 papillatus and macrostoma furnish a slight exception to this rule. 



Though the muscles of the body wall are relatively powerful, their 

 attachments to the subcuticle are not a conspicuous feature ; hence longi- 

 tudinal striae due to this cause, though of rather common occurrence, are 

 not very readily observed. There are no longitudinal striations in the 

 cuticle proper. This apparent complete absence of dermal markings often 

 imparts a glassy appearance to living mononchs when examined casually 

 under the microscope, an effect that is heightened by the fact that the 

 colorless body wall is, as a rule, of more than average thickness. Despite 

 their rather thick cuticle, mononchs are very flexible. They coil and un- 

 coil themselves with facility, a useful gift in a struggle with active prey. 

 Moulting. From researches on a considerable variety of genera, Mau- 

 pas concluded that nematodes undergo four moults, and that, correspond- 

 ingly, the life of each individual is divided into five periods. He exam- 

 ined no mononchs. The accompanying sketch of a portion 

 of the pharynx of a moulting Monochus brachyuris, from 

 Arlington, is therefore of interest, as indicating that this 

 specimen had yet to moult three times ; and since it was 

 already half-grown (0.8 mm. long) it is fair to presume it 

 had already moulted once, although of course there is no 

 proof of this. The sketch shows four successive dorsal 

 onchi, numbered in chronological order, each the represent- 

 ative of a separate cuticle. The fourth onchus is in a very lessive 'dorsal 

 rudimentary state. This record accords with the observa- :eth> *' 2> 3 ' 4 ' 

 tions of Maupas, and indicates the probability that mononchs also moult 

 four times. 



Strength and Activity. Various features of the cuticle and body- 

 muscles seem to stamp the mononchs as powerful nemas, and when they 

 are taken from their natural haunts and placed in a glass of water for 

 examination, their active serpentine movements fully justify the infer- 

 ence. Though less agile than species belonging to some other genera, 

 they are anything but sluggish. The movements of the anterior extremity 

 are especially striking, a certain suppleness of neck enabling them to 

 dart the head suddenly here or there in almost any direction, a faculty 

 enabling them with ease to capture their prey, even though it be active. 



Nemas Sometimes Float 



Distribution by flotation. Ditlevsen notes a very interesting trait of 

 his Mononchus spectabilis, namely, that of floating on the surface of 

 water. A number of free-living nemas belonging to other genera are 



