PART III : DESCRIPTION OF SPECIAL PARTS OF THE 



ANATOMY. 



A: THE VASCULAR LAMELLA. 



In Medusas it is a common thing to find that in certain definite 

 places of the gastro-vascular system two endodermal surfaces that were 

 primarily separated by a space have come together and fused into a 

 single lamella or plate. Such a structure is called indifferently a 

 cathammal plate, an endodermal lamella, or a vascular lamella. In the 

 adult animal the vascular lamella? are by virtue of their very nature 

 formations "with a past." They are scaffolding left in the completed 

 structure, giving us clues as to the way in which that structure was 

 brought about ; and in the Cubomedusa?, whose development is as yet 

 unknown, they therefore afford an unusually interesting subject for 

 special consideration. 



The vascular lamella that are found in Charybdea and Tripedalia 

 may for convenience be described as forming two systems, the internal 

 and the marginal. The former comprises the endodermal fusions that 

 separate the stomach from the stomach pockets (except for the spaces of 

 communication left free, the gastric ostia) and those that separate the 

 stomach pockets from one another. The marginal system consists of 

 the lamella that connects endoderm of the gastro-vascular system with 

 ectoderm of the surface in a ring all around the bell margin, and with it 

 also the vascular lamella of the sensory niche, which has already been 

 referred to in the general description of Charybdea. The lamella? of the 

 internal system have been described by previous writers, and especially 

 by Glaus in his paper on Charybdea, but they are still in need of compre- 

 hensive and clear treatment. The lamella? of the margin and of the 

 sensory niche have also been described by Glaus, but not thoroughly or 

 with entire accuracy, nor did he recognize the vascular lamella? of the 

 sensory niche as originally a part of the lamella? of the margin. This last 

 was first determined by H. V. Wilson upon specimens of Chiropsalmus 

 quadrumanus obtained at Beaufort, North Carolina. Professor Wilson's 

 unpublished notes on Chiropsalmus were very kindly placed in my 



