36 



PORIFERA. II. 





Xearest to the foreign body the skeleton is least regular, but a little farther out regular fibres occur 

 running parallel to each other, continuing to the surface, and piercing the dermal membrane. These 

 fibres are polyspicular with rather many spicules alongside, most frequently six to eight; with regard 

 to this fact, however, some difference may occur in different individuals, so that the fibres may contain 

 both fewer and more spicules. The distance between the fibres is about cri2 mm , and the average thick- 

 ness of the fibres may be given as o-035 mm . Coherent transverse fibres are not formed, but between the 

 primary fibres transverse spicules are found, most frequently singly, and without any regularity. Some- 

 times a tendency towards a more regular net of meshes may appear towards the surface. In many of 

 the individuals the primary fibres do not pass straight towards the surface, but show a tendency to turn 

 upward towards the upturned end of the sponge, so that the fibres in the egg-shaped roundgrowing speci- 

 mens may radiate to all sides, but at the same time turn upward, so that it may be seen, especially 

 in a longitudinal section, which end of the sponge has been turned up, and which has been turned down- 

 wards. Spongin is found in the fibres, but only to a small amount, and it is exeedingly white and clear. 

 Sptcnla: a. Mcgasclera are styli; they are more or less, often rather much, curved, and the 

 curve is almost always nearest to the upper end. The other end passes evenly into a point of middle 

 length, the outer end of which is most frequently somewhat shorter pointed. The needles are thickest 

 about the middle, also tapering somewhat towards the rounded end, and being thus a little fusiform. 

 The length is between o-i66 mm and o-3i ram , but in many individuals the ueedles do not vary so much; 

 thus individuals are found in which they reach no greater length than cr23 ram . Also the thickness is 

 somewhat varying, from croo6— o-n mm , and also in this respect some difference is found in different in- 

 dividuals. The thickest spicules are not always the longest ones. Besides the fully developed forms 

 developmental forms of every degree of thickness occur, and in some individuals these forms are 

 found in large numbers scattered in the tissue outside of the skeleton formed by the fibres; they were 

 found down to an exceeding fineness, less than o-ooi mm , and developmental forms of this thickness were 

 measured to a length of 0-15"™. The developmental forms, in contradistinction to the fully developed 

 ones, are long pointed. The individuals copiously provided with developmental forms of the styli 

 seemed upon the whole to be in a state of lively formation of spicules, developmental forms of the 

 chelae being also seen abundantly, b. Microsclera are only of one kind, anisochelsepalmatse. They 

 are characteristic by the smaller end being comparatively large, larger than is common in the Mycale- 

 anisochelae. Their shaft is straight, and they are otherwise of the common type; the alee of both ends 

 are highly folded round on the side; the tooth of the larger end is narrower than the alse and 

 rounded at the end; the tooth of the smaller end is of the same breadth as the alse, and it is some- 

 what pointed, which seems to be owing to the fact that the axis continues quite to the point of the 

 tooth; the alse of this end pass to the shaft in such a way as to make their upper or free edge 

 parallel to the upper edge of the tooth. In each end an oblong tuberculum is found. The chelse 

 vary not a little in size and also in form; thus they may be more broad or more narrow, and the 

 comparative sizes of the ends may be somewhat different; in a few cases there is almost no difference 

 between the two ends, so that the chelse approaches an isochela in form; generally, however, they are 

 not to be confounded with isochelse, as it is most frequently only the teeth that are of equal or about 

 equal size, while the alse of one end continue to be smaller than those of the other, as shown in 



