( 587 ) 

 EECOED 



OF CURRENT RESEARCHES RELATING TO 



INVEETEBEATA, CEYPTOGAMIA, MICEOSCOPY, &c.* 



ZOOLOGY. 



A. GENERAL, including- Embryology and Histology 

 of the Vertebrata. 



Development of the Vertebrate Eye.f — Professor Lankester 

 directs attention to the myelonic or cerebral eye which the Ascidian 

 tadpole possesses in common with all Vertebrates. All other animals 

 which have eyes develop the retina from their ectoderm. It is easy to 

 understand that an organ which is to be affected by the light should 

 form on the surface of the body where the light falls. It has long been 

 known as a very puzzling and unaccountable peculiarity of Vertebrates, 

 that the retina grows out in the embryo as a bud or vesicle of the brain, 

 and thus forms deeply below the surface and aioay from the light. The 

 Ascidian tadpole helps us to understand this, for it is perfectly trans- 

 parent and has its eye actually inside its brain. The light passes 

 through the transparent tissues and acts on the pigmented eye, lying 

 deep in the brain. We are thus led to the conclusion — and ho 

 believes this inference to be now for the first time put into so many 

 words — that the original Vertebrate must have been a transparent 

 animal, and had an eye or pair of eyes inside its brain, like that of 

 the Ascidian tadpole. As the tissues of this ancestral Vcrtebrato 

 grew denser and more opaque, the eye-bearing part of the brain was 

 forced by natural selection to grow outwards towards the surface, in 

 order that it might still be in a position to receive the influence of 

 the sun's rays. Thus the very peculiar mode of development of the 

 Vertebrate eye from two parts, a brain-vesicle and a skin-vesicle, is 

 accounted for. 



Embryolog^y of Batrachians.;}: — These 'New Researches' of 

 Professor Van Eambeke consists of two jiarts : (I.) on the envelopes 

 of tlio egg and external embryonic changes of Tritons and Axolotl, 

 and (II.) on the cleavage of the egg in Batrachians generally. 



I. 1. Having in a previous essay described the egg proper (vitel- 

 line splicro or globe) the author now distinguishes its five envelopes 

 as (1) the vitelline membrane, (2) chorion, (3) inner capsule, (-i) outer 

 capsule, and (5) adhesive layer. The first is thin and structureless, 



* i^' It sliould bo understood that the Society do not liold thonisolveH respon- 

 sible for tlic views of the autliors of the luipers, &e., referred to, nor fi>r the manner 

 in wliicli tliose views may be expressed, the objiet of the Kecord Ix'inj^ to present 

 a siimnmry of the pajjcrs us acbialhi published. Objections and corrections shouhl 

 therefore, for tlie most pait, be address( d to tiie aullii>rs. 



+ 'Degeneration: a rhapter in Darwinism ' (8vo, I/indon, 1S80). 



X ' Arch, dc Biologie,' i. (1880; pp. 305-380 (4 plates). 



