28 THE VOYAGE OF H.M.8. CHALLENGER. 



network (fig. D = fig. 27). This condition of tlie surface was most conspicuous about the 

 anterior part of the body, but the Ijody was much lacerated by the meshes of the trawl, 

 and, therefore, I cannot say whether the whole integument is in this condition in the fresh 

 state or not. The folds and plaits in the integument are so sharp that they give the 

 appearance under the microscope of somewhat spindle-shaped bodies with sharply pointed 

 extremities (fig. c, 1, 2, 3 = fig. 2G). At first I supposed that these bodies were urticating 

 organs, resembling those of BipaUum, but on carefully teasing up a portion of the integu- 

 ment with fine needles, and being unable to isolate a single one, I concluded that they 

 were mere folds. They are, however, of remarkable appearance, from their extreme 

 abundance and the manner in which they cross each other at all angles. They are well 

 preserved in glycerine preparations of the skin hardened in picric acid. 



" Beneath the integument is some granular glandular matter. Immediately beneath 

 the integument, and in close adherence to it, is the muscular tunic, evidently the 

 homologue of the cutaneous muscular system of Bipalium and other Planarians. As in 

 these, the outermost fibres are circular in direction, the inner longitudinal. 



" The muscular tunic encloses the entire body. It is thin, and in the fresh condition 

 of the animal transparent and inconspicuous, but becomes opaque when the animal is 

 hardened in picric acid. The iuner longitudinal layer consists of stout bands of fibres 

 running parallel to one another. The outer circular fibres are far less developed, and are 

 not gathered into bundles, but cross one another slightly obliquely in their transverse 

 course, forming a slight meshwork over the longitudinal fibres. 



" Beneath the muscular tunic and between its meshes the body mass is filled up with 

 a gelatinous, hyaline, structureless matter, imbedded in which lie the viscera and the 

 muscles attached about the orifice of the sheath of the proboscis. Internal muscles, except 

 those referred to, were not observed. 



" No eyes or other sense-organs were found, and ciliated sacs were not seen. 



" From the circumstance of the only specimen of Pelagonemertes having been much 

 lacerated, and from the animal not having been dissected, it will of course require further 

 examination. In the specimen as procured there was a deep constriction of the body at 

 about the junction of the first with the second fourth of its length. This, it appeared 

 pretty evident, had been caused by the meshes of the net. The posterior extremity 

 was somewhat injured, and its form may not be Cjuite correctly given. Ciliated sacs 

 may be present, and the structure of the proboscis might throw light on the affinities of 

 the animal. 



" The form of the digestive system is the most remai'kable feature about Pelago- 

 nemertes in its close resemblance to that of Dcndroccela. In other respects Pelago- 

 nemertes is thoroughly Nemertine in structure, being merely modified for pelagic existence. 

 It is remarkable that the gelatinous hyaline mass of the body is not tegumental in 

 character, but apparently homogeneous with internal structures. 



