October 7, 1898.] 



SCIENCE. 



483 



■Conant the marginal lamella. Unlike the true 

 vascular lamella, which simply connects one 

 «ntodermal cavity with another, the marginal 

 lamella extends from the entoderm of the gas- 

 trovascular space to the ectoderm of the bell 

 margin. It is a narrow strip which follows 

 -the outline of the marginal pockets, traveling 

 in the radii of the sense organs far away from 

 the actual edge of the bell, and surrounding the 

 «ense organs in such a way as to Indicate clearly 

 that they were once at the bell margin. The 

 marginal lamella seems to be a functionless, ru- 

 dimentary organ. Olaus, whose imperfect de- 

 scription of the structure did not bring to light 

 its morphological interest, as indicating the site 

 •of the ancestral bell margin, suggested that it 

 was perhaps the vestige of a ring canal. Conant 

 naturally is skeptical of this explanation of a 

 lamella connecting ento- and ectoderm. The 

 true meaning of this peculiar lamella is a point 

 well worth working up, more especially as it is 

 not confined to the Cubomedusae, but has been 

 observed in the ephyra lobes of discophores 

 {Bhizostoma). 



Before leaving this subject of the general 

 hody-plan, it may be mentioned that while the 

 probability is that the Cubomedusee are de- 

 scended from stalked ancestors {Luceruaria-Mke 

 forms), and hence that the apex of the exum- 

 brella was once drawn out into a peduncle, 

 there is in the adult Cubomedusa no trace ex- 

 ternally nor internally of this hypothetical 

 stalked condition. Light on this very interest- 

 ing point can only be expected from a study of 

 the development. 



Unlike the other Scyphomedusse studied, the 

 Cubomedusae possess a nerve ring. In their 

 study of the nervous system Claus and Conant 

 both depended on sections, and naturally the 

 results are not so satisfactory as those reached 

 by the Hertwigs on the Hydromedusse mainly 

 with the aid of macerations. Claus describes 

 the neuro-epithelium as consisting of alternating 

 supporting cells and sensory cells, the inner 

 ends of the latter becoming continuous with the 

 nerve fibres. Conant makes it doubtful whether 

 this is the actual condition, since he does not 

 find the sensory cells. He ofiers, however, no 

 observations on the origin of the ' nerve fibres. ' 

 Macerations will probably show the connection 



of these fibres with at least some of the neuro- 

 epithelium cells. 



The possession of a nerve ring has been re- 

 garded (Claus) as a point of essential similarity 

 between the Cubomedusae and the Craspedota. 

 The main ring in the former group is obviously 

 a differentiation of the subumbrellar epithelium, 

 and Claus, therefore, interprets it as homolo- 

 gous with the inner Craspedote ring. In the 

 immediate neighborhood of each sense organ 

 there are given off from the main ring two roots 

 which ceasing to be superficial bands pass through 

 the jelly, and emerge on the outer wall of the 

 bell (on the floor of the sensory niche). They 

 converge and unite, forming a superficial nerve 

 tract which crosses the base of the sense-club. 

 These four isolated tracts are regarded by Claus 

 as the remnants of a once continuous exum- 

 brellar ring, such as is found in the Hydro- 

 medusae, and which here, as in the Hydrome- 

 dusae, stands in connection with the subum- 

 brellar ring though the medium of fibres that 

 perforate the jelly. Conant, on the other hand, 

 regards the tracts lying across the bases of the 

 sense organs as portions of the primitive sub- 

 umbrellar ring which were shut off from the 

 main ring, when the marginal lobes grew to- 

 gether. With the Hertwigs and Haeckel he 

 thus looks on the ring as not homologous with 

 that of the Craspedota, but as a special differ- 

 entiation of the subumbrellar plexus found 

 throughout the Scyphomedusae. 



The sense organs of the Cubomedusae are 

 ' sense-clubs,' or modified tentacles. In addi- 

 tion to the crystalline sac, the expanded head 

 of the club bears six eyes. Four of these are 

 simple, but two are complex organs provided 

 with a cellular lens and cornea, a vitreous body 

 behind the lens, and a retina. These eyes look 

 into the bell cavity. It is especially in refer- 

 ence to the structure of the retina and vitreous 

 body of the complex eyes, that Conant's conclu- 

 sions differ from those of Schewiakoff. The 

 vitreous body Conant finds is not a homogeneous 

 structure, but is composed of prisms of re- 

 fracting substance. The retina does not show 

 the two types of cells (sensory and pigmented) 

 distinguished by Schewiakoff. Conant's results 

 in this matter of the retinal structure are in 

 some respects negative. The points still to be 



