74 Miscellaneous. 



convex portion, the margin of the latter glides back over the more 

 coarsely cellular endodermal mass, and coats it, just as an ectoderm 

 does the endoderm, in a sterrogastrula. Possibly this is only ap- 

 parent, the peripheral cells of the posterior mass merely joining 

 themselves to the anterior convex layer by a corresponding meta- 

 morphosis. At any rate the endoderm of the larva, shortly before 

 its attachment, consists of a sacciform tbin layer posteriorly en- 

 closing the coarsely cellular mass, and anteriorly the cavity; at its 

 inner surface it secretes a distinct cuticle, by which it is always 

 recognizable. Its cells also provide for the above-described ad- 

 hesion of the larva, especially in the periphery of the flat disk ; 

 from this marginal zone the layer becomes condensed by the ap- 

 proximation of its loosely reticulate mass of cells beneath the 

 vanishing ectoderm, to form an epithelium as the cuticle of the 

 sponge. The osculum and the pores originate in exactly the same 

 way as enlarged spaces between the cells. 



During the attachment of the larva the whole arch of the endoder- 

 mal cavity becomes compressed, and, on the other hand, the inner 

 endodermal mass advances into it, until it disappears with the 

 exception of a fissure-like space between the cuticle and that mass, 

 extending more or less distinctly over the whole upper surface of 

 the sponge. In the middle of the still disciform body, however, this 

 fissure-space becomes enlarged into a deep round pit beneath the 

 strained cuticle by the depression of its bottom formed by the above- 

 mentioned inferior parenchyma. This cavity becomes lined by some 

 free cells with an epithelium resembling the cuticle, and acquires one 

 of the above-mentioned apertures in its covering (cuticle). Around it 

 .there are then produced some similar pits, in part also furnished 

 with similar apertures, of which the oscnlum is characterized by its 

 margin being elevated like that of a crater. Although all these pits 

 originally communicate with each other as depressions of the sub- 

 epidermal fissure-spaco, they are afterwards entirely or partially 

 separated from each other by their linings, which extend up to the 

 cuticle (afferent and efferent canal-system). 



In the meantime, however, the flagellate chambers are produced in 

 the parenchymatous endodermal mass. They are genetically quite 

 independent of the above cavities, as their separated rudiments 

 already exist in the larvae. These foundations originate from parti- 

 cular endodermal cells, around the primitive nucleus of which 

 several new small nuclei arc produced without any recognizable phe- 

 nomena of division. Corresponding to these nuclei buds of the 

 mother-cells are produced, and from these cell-aggregates, which 

 arrange themselves iu capsules and usually coalesce in groups to 

 form more or less closed hollow spheres. These spheres, which are 

 afterwards ciliated within, unite, sometimes directly with the above- 

 described cavities, sometimes with inward diverticula from them, or 

 with irregular canals, which, like the cavities, originate as inter- 

 cellular spaces lined with pavement epithelium, but independently 



