150 Mr. W. S. Kent on the Emhryology of Sponges. 



a young sponge shortly after this first attachment, the ampul- 

 laceous sacs in these sponge-forms, when they occur, are con- 

 fined entirely to the basal region, and are evidently developed 

 from the posterior root-cells. 



Although the embryonic form last discussed, and which, 

 from its peculiar contour and aspect, might be denominated 

 the acorn-form, represents the most conspicuous and constantly 

 recurrent deviation from the normally ovate type, innumerable 

 other variations occur, presenting an altogether irregular and 

 Tinsymmetrical shape. One of these irregular variations is 

 represented at Plate VI. fig. 17, and another at fig. 18. In 

 the latter of these certain of the cellular units have developed 

 their flagellate appendages, while the others present the 

 amorphous rounded form characteristic of those of the lower 

 portion of the acorn type. In the former example a nest- or 

 cup-like shape is assumed, not unlike the basal portion, taken 

 separately, of the acorn variety, and in which the zooids are 

 for the most part fully matured. Other variations might be 

 figured and described without number; those given, however, 

 suffice for the required purpose, that of demonstrating the 

 non-persistency of contour of these so-called embryonic bodifes. 

 In addition to variation in contour, these same structures will 

 be found even in one sponge-stock to vary among themselves 

 considerably in calibre, notwithstanding that the component 

 units or zooids exhibit a corresponding phase of development. 

 Some of these bodies are several times larger than others, and 

 contain necessarily a very much greater number of separate 

 units. This non-conformity of the size of these unit-aggrega- 

 tions of like age appears to admit of two constructions. In 

 the one case it seems highly probable that the primitive 

 rounded Amoeha-\\k& mass from which these compound bodies 

 are developed is built up, previous to its assumption of a qui- 

 escent state and subsequent segmentation, through the fusion 

 or coalescence of a variable number of the original and 

 typical collar-bearing zooids with which the sponge-cavities 

 are lined, and in a manner parallel to that of the in- 

 dependent monad form illustrated by Plate VI. figs. 27 

 to 33, in which sometimes two only and sometimes a 

 much larger number of zooids coalesce and produce by a 

 corresponding process of segmentation a larger or smaller 

 number of daughter zooids or macrospores resembling the 

 parent. The coalescence of two Amoeba-\\\K.Q sponge-units 

 has been frequently observed ; and it is not unreasonable to 

 premise that a similar welding with one another, as in tl»e case 

 of the simpler monad, of a larger number of similar units is 



