NOTES ON THE PHOTOPHORES OF SERGESTES PREHENSILIS BATE. 305 



haematoxylin moderately well ; and then, unless the sections are excessively 

 thin, it presents a distinctly darker appearance than the underlying cuticular 

 parts. Freeborn's picro-nigrosin gives it a yellowish-green color, while 

 the underlying parts assume a bluish color. 



The inner lens body (/ 3 ) forms the most bulky part of the entire lens, 

 measuring more than three times as thick as the outer lens body. It is of 

 a biconvex shape, being uniformly arched on the outer surface and some- 

 what flattened in the central major parts of the inner. It joins the inner 

 layer of the general euticula at the equator, very gradually on the outer 

 side but with a sharply angular demarcation on the inner. Unlike the two 

 other parts of the lens, the inner lens body shows the peculiarity of 

 differentiating itself into three strata, when stained with Congo red or with 

 Freeborn's picro-nigrosin. The strata are about equally thick. The 

 outer stratum takes up the stains to a moderate degree, the middle stratum 

 very weakly, and the inner stratum most strongly. However, when the 

 sections are too thin, or when staining reagents other than the two mentioned 

 are used, it frequently happens that the outer and the middle strata are 

 both about equally weakly stained and are thus scarcely distinguishable 

 not only from each other but also from the outer lens body, while the inner 

 stratum presents itself strongly stained and well set off from the middle 

 stratum. Under such circumstances one might easily mistake the inner 

 stratum for a part distinct in itself, and the middle and outer strata together 

 with the outer lens body for another single part of the lens. I should think 

 that this fact may have had to do in leading both Hansen ('03, p. 74) and 

 Kemp ('10 b, p. 641) to regard the lens in 6". challetigeri to be composed ot 

 an outer biconvex and an inner concavo-convex parts, which, at any rate, 

 does not fit with the state of the thing in 5. prchensilis. Likewise, the 

 " middle layer " described by Kemp from the lens of Acanthephyra debilis 

 and held by him to be distinct from the inner lens layer, is not improbably 

 nothing else than the strongly differentiated outer strata of the inner lens 

 body. In passing it may be noted that the entire lens in 5". prehensilis is 

 perfectly colorless, differing in this respect remarkably from the same of 



