322 THE VOYAGE OF H.M.S. CHALLENGER. 



of the specimen docs not allow of the minute structural details being made out, but it 

 appears not improbable that the vertical striation of the superficial layer is the expression 

 of a structure somewhat similar to that described above in Oj^ostomias micripnus. 



y. The larger posterior organs. — These organs are similar to the foregoing, but the 

 reticulate glandular layer is absent. The light-reflecting spicule-layer encloses the 

 proximal, immersed, spherical portion of the organ (PI. LXXI. fig. 28, c) and does not 

 extend beyond the constriction, which is more conspicuous and deeper than in the 

 smaller anterior organ. Here the spicide-layer, which is 0"4 mm. thick in the 

 fundus, terminates in a thin margin. This proximal portion of the organ has the 

 shape and size of a pea, and lies below the posterior end of the superficial portion. 

 The spicule layer is perforated by very numerous, slightly branched, more or less 

 oblique canals, which have a circular transverse section and are on an average only 

 O'Ol mm. wide (PI. LXXI. fig. 31). These are occupied by nerves and bloodvessels. 

 The contents of the proximal portion, that is to say, the part surrounded by the spicule- 

 layer, is a large, somewhat irregular gland. The gland-tubes, which are comparatively 

 uide, having an average diameter of 0"05 mm., appear to commence in an irregular 

 tangential position close to the spicule-layer, and they converge in the interior towards 

 the narrow neck, where the proximal and distal portions of the organ are joined 

 (PI. LXXI. figs. 28, d, 31). Between the gland-tubes comparatively thick layers of 

 fibrous tissue are met with, which contain nerves and large bloodvessels. The superficial 

 portion of the organ shows the same vertical striation which has been described above in 

 the smaller anterior organ. In this case also the indiff"erent state of preservation pre- 

 cludes a precise account of the minute structure being given. 



c. Innervation. 



(1) In general. — As mentioned above, the nerves which are found in these organs 

 enter them in the shape of a stout bundle. They spread out to form a ners^ous plexus, 

 which either appears as a film on the outer side of the spicule-layer in the posterior 

 organs, or sends its branches along the threads in the reticulate portion of the organ 

 below the spicule-layer in the anterior organ. Fine branches of the nerve penetrate the 

 spicule-layer and enter the distal portion of the organ, where they can be traced for some 

 distance in the fibrous tissue which surrounds the gland -tubes. The superficial portion 

 of the larger posterior organ of Pachystomias microdon is supplied by a special nerve 

 (PI. LXXL fig. 28). 



(2) The hrain of Echiostoma harhatum. — In this species the suborbital phos- 

 phorescent organs are highly developed. I have dissected the brain of this species to 

 ascertain what nerve supplies the suborbital organs. The brain (PI. LXXII. fig. 42) 

 exhibits for the most part no striking peculiarity. The Nervi Olfiictorii (i) are dilated 



