E. MAESHALLT. — YOUNG SPECIMENS. 113 



imperforated by the parietal oscula (p. 107). Here a number of 

 fine circular bands, composed of yet weakly developed parenchy- 

 mal spicules, lie most closely together, attesting their recent 

 formation as was pointed ont by F. E. Schulze ('95, p. 25). On 

 tlie other hîind, specimens of over, say, 100 or 120 mm. length, 

 no longer show tliis peculiar characteristic in the corresponding 

 roo-ion, althontrh this mav still be somewhat backward in the 

 general development of its parts. The last transverse beams at 

 this end of the sponge stand more or less distinctly apart, or 

 at any rate never so close together as in an earlier period of 

 growth, and the very last beam is commonly separated from the 

 superior ritn of the lateral wall by a space which is traversed 

 only by oblique or longitudinal beams that directly pass above 

 into the sieve-plate beams. Parietal oscula are now met with 

 right up to the border of the sieve-j^late. (See upper part of fig. 

 4, PL IV). To all appearances, then, the marginal region, as 

 also the parts further below, is no longer giving rise to new 

 transverse beams, although the possibility of, so to speak, sporadic 

 new-formations can not be altogether excluded. To sum up : 

 the transverse beams develop to their maximum number before 

 the sponge-body has grown to a length of about 100 mm. During 

 its subsequent growth, the beams should go only wider and wider 

 apart from one another, their number remaining practically 

 stationary or nearly so. 



Turnius; now to column I of the table, the above fact seems 

 foreshadowed in that some of the highest figures are already met 

 witli before the specimens attiin a length of lOvO mm. The fall 

 of figures for larger specimens, observable in the table, is prob- 

 ably to be explained as mainly due to individual circumstances 

 and not to actual decrease in number. However, I am inclined 



