E. MARSHALLI.— YOUKG SPECIMENS. 107 



Oil the greater part of the body including the lower end. Toward 

 the upper end, they gradually become smaller, while at the same 

 time the external depressions closed at the bottom become more 

 and more frequent. In some of the depressions the oscula are 

 found in the first stage of breaking through. The ledges become 

 superiorly less and less prominent, until finally at a short dis- 

 tance before reaching the superior edge of the lateral wall they 

 cease altogether to exist. So that, there remains at this terminal 

 region an even-surfaced, unperforated zone of nearly uniformly 

 compact appearance, — a zone retaining the characteristics of the 

 wall in a much earlier developmental stage. 



Such a plain-looking marginal zone is observable up to a 

 stage when the sponge measures about 70 or 80 mm. in length. 

 So long as it persists and also for some time after it has become 

 perforated by newly formed parietal oscula, the soft cuff proper 

 is slightly or not at all developed. This develops distinctly after 

 the ledge formation, which follows that of the parietal oscula, 

 has extended to the u23permost rim of the lateral wall. Never-- 

 theless, I find this rim in all young specimens before they acquire 

 the true cuff not quite thin and sharp, but possessing a firm 

 narrow edge squarely cut off (seethe upper end of fig. 7). This 

 is due to the fact that many of the slender parenchymal spicules 

 composing the longitudinal skeletal beams and coming up to the 

 rim are exceedingly elongated sword-like hexactins, of which the 

 five relatively very short rays, corresponding to the hilt and the 

 guard, are situated in a row at the very edge of the lateral 

 wall. Strange to say, I have not succeeded in finding the same 

 parenchymal hexactins in full-sized specimens. This may how- 

 ever be explained by assuming that the said hexactins after a 

 certain period neither grow in size nor increase in number, anc]. 



