174 SUMMARY OF CURRENT RESEARCHES RELATING TO 



He also found in a seven days' rabbit embryo a rudimentary 

 neurenteric canal, in tbe form of a shallow pit, in the epiblast at the 

 front end of the primitive streak. 



4. The notocliord is formed of an axial strip of cells, which under- 

 lies the epiblast of the medullary groove, and which either never 

 become divided into mesoblast and hypoblast, or in which such a 

 division, if it does take place (as appears not impossible), is very soon 

 lost. This strip of cells is originally continuous laterally with both 

 mesoblast and hypoblast, but as the lateral mesoblast becomes con- 

 verted into definite vertebral plates, the connection is lost. 



There can, it is believed, be no doubt of the connection of the 

 lateral hypoblast and mesoblast with the notochordal cells in the 

 mole ; in the rabbit, Mr. Heape is inclined to believe that a similar 

 connection is present, but his evidence on this point is not yet 

 conclusive. 



Development of AmpMoxus.* — In this paper Dr. B. Hatschek 

 deals in detail with the earlier stages only. In describing his 

 method of study, he says that he has always endeavoured to study 

 in the living object all that it would allow. For the preservation of 

 specimens in the cleavage stage Kleinenberg's fluid was found useful ; 

 and coloration was effected by osmic acid : the former was not 

 adapted for the gastrula-stage, when osmic acid was used. The 

 earlier stages of segmentation require a treatment different to the 

 later, on account of the large amount of yolk then present ; an addi- 

 tion of ^ per cent, osmic acid to the sea-water killed the embryo in 

 the earlier stages, when no colouring matter was employed ; in the 

 later stages Beale's solution or picrocarmine were found useful. 



Oviposition is seen to be markedly dependent on the weather and 

 the time of day ; the generative products are most certainly expelled 

 by the mouth. Development breaks up into two well-marked stages, 

 the one embryonic, when it is effected at the cost of the nutrient 

 material contained in the egg, and is very rapid. At the close of this 

 period the mouth is developed, and the first gill-cleft. The larva 

 now begins to feed itself, its cells contain transparent protoplasm, and 

 the developmental processes are very much slower. 



While giving a general support to Kowalevsky's classical account 

 of the earlier stages, the author finds that the ova are generally quite 

 isolated. The five fat-bodies of the Russian author are regarded as 

 yolk-granules ; the spermatozoa would appear to always enter at the 

 vegetative pole. The cleavage was found to be unequal, the differences 

 between the two poles being well marked. There is a pause of about 

 an hour between the formation of the first and of the second groove. 



At the blastula-stage we find the investing cells taking on an 

 epithelial character, till there is formed a general outer layer, enclosing 

 a cavity. This simple epithelium forms the substratum for the later 

 developmental processes ; all the essential organs are formed by 

 foldings or outgrowths from it. Bilateral symmetry is obvious at a 

 very early period ; the blastopore appears to close from before back- 



* Arbeit. Zool. Inst. Univ. Wien (Clans) iv. (1881) pp. 1-89 (9 pis.). 



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