Development op halisaroa lobularis. 019 



only the genus Hal is arc a, and this should be divided into 

 two, for Halisarca lobularis and Halisaroa Dujardinii 

 differ far more from one another than is consistent with specific 

 distinction merely. A fundamental difference is to be found 

 in the character of the canal system in the two Sponges, and to 

 this may be added the difference in the character of the ecto- 

 derm and the presence of skeletal fibres in H. Dujardinii, 

 which are absent in H . lobularis. But it is needless to insist 

 on this point further, as I find since writing this paper that 

 Vosmaeri has already conferred a new generic name (Oscar- 

 ella) on H. lobularis. 



March, 1884. 



EXPLANATION OF PLATE XXXVII, 



Illustrating Mr. W. J. Sollas's Paper - On the Development 

 of Halisarca lobularis" (O. Schmidt). 



The fio-ures were all drawn with camera lucida, but since the paper on which 

 they wer"e traced was placed considerably below the level of the microscope 

 stage they are enlarged to nearly twice the diameter that the lenses used for 

 each would otherwise indicate. 



Fig. 1.— Mature ovum. Zeiss, D Obj., No. 4 oc. 



rigs 2 to 14 and IG represent sections illustrating various stages in the 

 segmentation of the ovum. All drawn with a Ross 1-inch Obj, Zeiss, No. 4 

 oct except Figs. 8, 9«, 14«, and 16«. , , , , . , 



Fig. 2 -Stage of two segments, with structureless blastema shown on each 



side of the cleavage plane. 

 Fig 3.— An exceptional stage of three segments. 

 Fig! 4.-An exceptional stage of four segments, showing two opposite 



blastomeres united. 

 Fig. 5. -Normal stage of four segments, with surrounding blastema. 

 Fig. 6.— Section showing five segments. 

 Fig. 7.-Section showing si x segments, with surrounding blastema. 



1 Bronn's ' Thierrisch,' Bd. ii, pi. viii, article "Porifera." 



