Fostlarval Development of Leucosolenia variabilis, H. sp. 49 



10. 6. Section of stage of about the fourth day of fixation. 



cells are lacking. The gastral cells are at first elongated, but later 

 become shorter, and take on the characteristic appearance of collar 

 cells. I have not been able to make out whether all the gastral cells 

 become collar cells, or whether some of them do not become the 

 wandering cells of the adult, which seems very probable. The 

 osculum appears about the sixth day of fixation. 



The Development of Leucosolenia cerebrum, H, L. reticulum, 0. S., 

 and L. coriacea, Mont. 



These three species have larvae of the type with which we are 

 familiar from the descriptions of Metschnikoff * and Schmidt, f 

 namely, oval ciliated blast ulee, in which an inner mass is formed by 

 immigration of cells into the interior. The process is most easily 

 followed in the more transparent larva of L. reticulum (fig. 7), where 

 the modification of ciliated cells into granular cells, and their sub- 

 sequent immigration, takes place at the posterior pole. When the 

 larva is ready for fixation, a considerable quantity of granular cells 

 has been formed, though the cavity is far from being obliterated. In 

 the opaque larvae of L. cerebrum and coriacea the process is more 



* " Spongiologische Studien," 'Zeitschr. f. Wiss. Zool.,' vol.32, p. 362, Taf. 

 XXIII. 



f " Das Larvenstadium von Ascetta clatkrus und Ascetta primordialis" ' Arch. f. 

 Mikr. Anat.,' vol. 14, pp. 249263, Taf. XV, XYI. 



YOL. LX. B 



