^Fr. II. J. Carter on the Genus llossella. 113 



alimentary apparatus will afterwards be developed. Near the 

 boundary between tlie middle and the girdle-like jiarts this 

 layer entirely ceases, and in the girdle-like part (region of the 

 formation of the arms) and further to the ])ole of the nutritive 

 vitellus and round the latter we only meet with the cells of 

 the dermo-muscular layer, as has already been stated. Con- 

 sequently the lower or intestino-fibrous layer of the second 

 germ-lamella, as may easily be seen, originates by transverse 

 division of the oi'iginaliy one-layered second germ-lamella, and 

 therefore in the same way as the latter lamella itself from the 

 cells of the one-layered Ijlastoderm or the u])per germ-lamella. 

 The cells of both layers of the middle germ-lamella are always 

 rather smaller, but are more numerous than those of the upper 

 lamella. In form they are generally oval, not unfrequently 

 extended (in the wall of the yelk-sac) ; their protoplasm is 

 dark, fatty ; and the nucleus (or often two) enclosed in each 

 cell can scarcely be detected without reagents. None of the 

 cells of either the second or the upper germ-lamella contain 

 any trace of membranes. 



It is not without a purpose that I have dwelt so long on 

 the mode of formation, the individuality, and the distribution 

 of the first two gcrm-lamellas, seeing that the only extant 

 memoir treating of this subject (namely that of E. Metschni- 

 koff*) is not quite sactisfactory. In the first place, this 

 naturalist has not recognized the second or inferior lamella 

 (" parenchymatose ") as the middle one ; and secondly, he has 

 not referred to its cleavage into the two layers above described, 

 which play so important a part in the formation of the em- 

 bryonal organism. I regard it as almost unnecessary to add 

 that my wearisome investigations of the development of four 

 difterent species of Cephalopoda completely contradict the 

 opinion put forward by Kolliker f, according to which both 

 the germ-lamellae are denied to the Cephalopoda. 



[To be continued.] 



XIV. — On the Genus Rossella {a HexactinelUd Sponge), 

 with the Descriptions of three Species, By H. J. Carter, 

 F.R.S. &c. 



[Plate X.] 



In 1872 I published some figures of two forms of sponge- 

 spicule which were found abundantly adhering to fragments 

 of a Tethya ( T. antarctica, C.) that had been dredged up from 



• Loc. cii. p. 19. t Loc. rit. p. 107. 



Ann. dfc Mag. N. Uist. Ser. 4. Vol. xv. 8 



