ON THE HEAD KIDNEY OP BDELLOSTOMA. 129 



some glandular function may possibly be attributed to the large 

 chains of "botryoidal connective tissue" in which many of the 

 blood-vessels end.^ In Echinoderms, the abundance of 

 glandular cells in the cardiac plexus is probably a principa 

 cause of the whole organ being regarded by many observers as 

 an excretory apparatus. Among Molluscs, glandular struc- 

 tures, connected with the auricles, have long been known 

 among Cephalopods, while the glands of the pericardium of 

 Lamellibranchs, associated as they generally are with the 

 auricles and afferent vessels, are probably of the same nature.^ 

 Among Arthropods, the '' coxal glands," recently described 

 by Professor Lankester,^ may perhaps prove to be connected 

 with the vascular system, though the small blood supply at 

 present recognised is certainly against such a view. 



An investigation of the functions of these various structures 

 in Invertebrates can hardly fail to afford an important clue to 

 the real nature of the Vertebrate suprarenals. 



EXPLANATION OP PLATE XII, 



Illustrating Mr. W. F. R. Weldon's Paper " On the Head 

 Kidney of Bdellostoma, with a Suggestion as to the Origin 

 of the Suprarenal Bodies." 



Complete List of Reference Letters. 



B. Lining epithelium of a glomerulus, b.-c. Blood-corpuscles, b. m. Base- 

 ment membrane, c. Blood capillaries, cl. Blood-clot in ventral duct of bead 

 kidney. B, ep. Epithelium of central duct. gl. Glomerulus at posterior 

 extremity of head kidney, g^. First glomerulus of functional kidney, g". 



^ Lankester, " On the Vasifactive and Connective Tissues of the Medicinal 

 Leech," ' Quart. Journ, Micr. Sci.,' vol. xx, 1880. 



^ See Grobben, " Morphologische Studien iiber die Harnund Geschlechts 

 apparat, &c., der Cephalopoden," ' Arb. Zool. Inst. Wien,' v Bd., 18S3. 



3 " On the Skeletotrophic Tissues and Coxal Glands of Limulus, Scorpio, 

 and Mygale," ' Quart. Journ. Micr. Sci.,' Jan., 1884. 



