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of the body ; Dr. Haacke is, however, careful to point out that this 

 " bilaterally-symmetrical" stage is not to be confounded with that 

 which obtains in the Vertebrata, for the latter are only comparable to 

 a single paramere made up of two antimeres set on either side of a 

 median plane, while in the coral there are two parameres even at this 

 stage ; two new sarcosepts then apj^ear and the larval becomes tetra- 

 l^leural, and this stage is followed by the hexamphipleural stage, 

 which is only of short duration ; other sarcosepts are developed, and 

 twelve can shortly be made out ; hereafter, in some forms, the number 

 of sarcosepts is increased. As to the cause of this ajjparent bilateral 

 symmetry, the author considers that the dipleural form of the Vermes 

 and other Bilateria is to be easily referred to a creeping mode of life, 

 to locomotion in a definite direction, while the regularly pyramidal 

 form is due to adajjtation to a sessile mode of life.* 



In conclusion, he points out the natui-al characters of the group 

 of the Octocoralla, which never have either more or less than eight 

 tentacles and sarcosepts ; while the difficulties as to the Hexacoralla 

 are resolved by showing that the number six recurs with sufficient 

 constancy to justify us in believing in the arrangement having been 

 transmitted from a six-rayed ancestor ; this arrangement may, how- 

 ever, have become subsequently obscured by the formation of a larger 

 number of sarcosepts. 



Porifera. 



Spongiological Studies.t — A paper under this title has just been 

 published by Professor E. Metschnikoflf. 



1. Developnent of Halisarca Diijardinii. — Of the two Neapolitan 

 varieties investigated, one corresponded with F. E. Schulze's descrip- 

 tion, while the other was distinguished by forming thin, soft, slimy 

 incrustations on stones. The larvae of the two were similar, except 

 that that of the first was twice as large as that of the second. The 

 sjiermatozoa of the adult occurred in seminal capsules with a distinct 

 epithelial investment. The younger eggs were beset with large club- 

 shaped processes of their substance, standing out at right angles to 

 the surface, and completely disappearing as the egg reaches maturity. 

 No true vitelline membrane was observed, but a thin investment to the 

 egg existed, probably formed of endothelial cells. 



Yolk-division is complete. The first four blastomeres are similar, 

 but afterwards a distinction is observable in larger and smaller masses 

 arranged radially around the blastocele. The latter is at first small, 

 becoming practically obliterated at one stage of division, but latterly 

 appears again, and increases in size, the larva then consisting of a 

 single layer of cylindrical cells surrounding a large central cavity. In 

 this cavity, a number of cells now appear, constituting the mesoderm ; 

 their exact mode of origin was not ascertained, owing to the opacity 

 of the embryos. The mesoderm cells are of two kinds, ordinary, finely 

 granular cells, and " rosette-cells," with large, highly-refracting gra- 

 nules : these latter are by far the more numerous and undergo rapid 

 multiplication, completely filling up the segmentation cavity. 



* Cf. Ilatscliek, tliis Journal, ante, p. 5C7. 

 t ' Zcitscbr. wiss. Zool.,' xxxii. (1879) p. 349. 



