506 HYATT'S REVISION OF THE 



lateil or not, could not be seen in specimens so long preserved in liquor. On one pole of this 

 larva there was a circular space of variable size loaded with dark pigment, and made up of 

 apparently larger and rounder cells, at least that was their external or superficial aspect ; 

 they were not seen in section. This area became more definitely restricted and more sym- 

 metrical in outline in the next stage, and finally a distinct constriction separating it from 

 the rest of the larva became visible. About the same time, or even previous to this, in 

 some specimens a clear, round space appeared in the centre of this area, which I shall for 

 convenience sake call the "basal" area, and the darker zone about it the basal collar. In 

 the next stage a constriction or depressed line separates the basal area from the collar, 

 which then stands out as a distinct raised ring, somewhat depressed along the central line 

 by a slight sulcation in most specimens, but not in all. Sometimes the basal area in these 

 alcoholic specimens is depressed considerably below the surface of the basal collar, but more 

 frequently' it is considerably raised above it, and this seems to be the normal condition at all 

 stages. 



The most curious folds take place in the larva from the contraction of the ectoderm, so 

 that I was completely deceived into the belief that they represented the earliest stage of 

 the development of the complicated fibrous skeleton in the first specimen I saw, which hap- 

 pened to be one with very symmetrical folds, or rather channels, on the surface. The larva 

 at this stage is still surrounded by the thin hyaline membrane previously noticed, and when 

 three or more are close together this capsular membrane becomes a prominent feature. 

 The cells composing it are of large size, in diameter about equal to the length of the 

 ectodermal cells. 



After the appearance of the pigment at the basal end, sometimes before the collar is formed, 

 and in some cases subsequently, a similar gathering of pigment is observable at the opposite 

 pole. Then probably at an equally variable succeeding period, the cells at this extremity take 

 on the rounded aspect externally of those of the basal collar, and the ectoderm becomes 

 decisively thinner at this place. I saw this in only one specimen, but it hajipened to be a 

 remarkably fine and unusually transparent form, showing the fully developed basal collar 

 and basal area. There was no aperture visible at this point, which might be called the 

 cloacal pole, though the central cells of the ectoderm were distinctly visible. 



It will be observed that these cursory observations are strongly confirmatory of those 

 made by Barrois upon his Verongia rosea, but not of his Gumminea f mimosa, the 3'oung 

 of which resemble more closely those of true Halisarca, as figured by Carter and observed 

 by Barrois and Carter, and have a significant resemblance to the young of the Calcispongite. 



The observations of Barrois upon Verongia rosea show about the same stages of devel- 

 opment as those of Spongia described in this paper, with the exception of his fig. 39, 

 which, as one of the last of the simple stages of segmentation, was not observed by me. 

 My observations have led me to regard the skeleton of the Keratosa as the product 

 primarily of the ectoderm, and those of Barrois previously quoted sustain this view. The 

 stages observed by me in Sjmngia graminea and corlosia correspond to Barrois' figs. 23, 

 27, 28 of the siliceous sponge on his PI. 15, and his figure on PI. 14 of Verongia rosea, 

 corresponds to fig. 26 of PI. 15. It is subsequently to this that the basal collar and area 

 are formed, and that the larva of Spongia assumes characteristics similar to those of the larva 

 of Chalinula, and some other siliceous sponges of the true Halichondrida observed l)y me at 

 Eastport, Maine ; but in none of the species of the siliceous sponges examined did I wit- 



