OF ARTS AND SCIENCES. 261 



two layers, a superficial broken stratum, of a brownish, hue, and 

 variable in thickness, which is separated by a sharp line from the 

 underlying homogeneous bluish layer. The latter is uniform in 

 thickness and regular in outline. These two layers are slightly 

 separated at the median lines, and between them may be seen 

 shreds of cuticular substance, which, to judge from tangential sec- 

 tions, lie in rows, and are apparently attached to the deeper layer; 

 they are probably the hairs of the adult. From these appearances 

 I feel justified in concluding that the outer layer is the last larval 

 cuticula, which is ready to be cast when the nematode leaves its 

 host, and the deeper layer is the permanent cuticula of the adult, 

 which already bears the characteristic hairs. Since this specimen 

 was practically as far developed as the youngest free form de- 

 scribed in the previous paper, it was probably nearly ready to 

 desert its host, and therefore furnishes no new evidence as to the 

 structure of the female. 



The discovery of this individual seems to establish bej r ond ques- 

 tion the parasitic nature of the young Nectonema, and indicates 

 Pala?monetes as its host. On the analogy of Gordius there is some 

 reason for supposing that Nectonema may have facultative hosts, 

 and it may even be that Palremonetes is only an occasional host; 

 yet that it is normally one can scarcely be doubted in view of the 

 maturity and perfect development of this specimen. Further, it is 

 more probable that the development is completed in a single host 

 than that a change of hosts occurs, and, in spite of the scarcity of 

 the parasite, one may confidently expect, now that the attention 

 of investigators has been directed to this host, that all stages of 

 the development will be obtained. 



The results obtained from the study of a single specimen are 

 necessarily incomplete, and are presented in order to call attention 

 to the host, in the hope that more material may be obtained, and 

 also to establish the position taken in my previous paper as to the 

 parasitic nature of the immature Nectonema. I expect to search 

 next summer for additional material on the development, and shall 

 be deeply indebted for any further information as to the occurrence 

 of this nematode or its host. 



Morphological Laboratory, 



• University of Michigan. 



