PORIFERA. II. 



upper end of the styli are not rarely formed as stated by Bowerbank with regard to M. constricta 

 and M. lingua; in this case a kind of handle is found on the spicule, the upper end being narrowed 

 for a shorter or longer way and then passing rather abruptly into the thicker part. This structure 

 of the spicule may be more or less marked, and is frequently almost imperceptible, and it is very 

 often quite wanting. The feature may, moreover, be different in different individuals, so that it is found 

 more frequently and more marked in one individual than in another. The needle is thickest in the 

 middle, and the tapering end runs into a point rather much varying in length as well in one indivi- 

 dual as in different individuals. The length of the styli varies from 0-447 — o7i5 mm and the thickness 

 from o-oio — o - oi6 mm ; these are the limits within which I have found the needle varying in the species, 

 but there may be some difference in different individuals, and in one individual the needles do not 

 generally show so great a variation. The limits most frequently found may be given as to length 

 0-5 — o - 65 mm , as to thickness croii— 001 $ mm . As before mentioned, the transverse spicules occurring out- 

 side of the fibres are oftenest a little shorter and thicker than those forming the fibres, and they are 

 curved. Finer developmental forms are only seen in small numbers. The dermal spicules are straight; 

 they are of a particular form, their thickest part being found nearest to the pointed end, while they 

 are evenly tapering towards the rounded end, which is often very slightly expanded. Sometimes at 

 the rounded end they may be of the same handle-like form, as is mentioned in the skeletal spicules. 

 While their size and the length of their point, and by these features to some degree also their form, 

 is rather constant in one individual, they vary not a little in different individuals. It is, however, 

 chiefly only the length of the point which is varying, but this fact again influences the form and the 

 length of the whole spicule. In some individuals the point is quite short or even rounded, and then 

 the thicker part of the spicule is found close to the point; in others the point is even and of a middle 

 length, and in others again very long, up to quite exceedingly long and thin; in the latter the thicker 

 part of the spicule is then found about in the middle. That it is really only the point that is of 

 varying length, is also seen by the fact that the longer the point, the longer is the spicule. The 

 length varies altogether in the different individuals from 03 — o'5 mm ; in the separate individuals it is, 

 for instance, 0-3— o^S" 1 ™, 0-35 — 042™'", 042— o - 5 mm , and these lengths are quite corresponding to the 

 smaller or greater length of the point. The thickness, which is also a little varying, as well in the 

 species as in the separate individual, is O'OC^— o-oi mm . b. Microsclcra are auisochelse palmatse, sigmata, 

 and rhaphides in trichodragmata. 1. The anisochelse are of the common Mycale-type; the shaft is 

 slightly curved, the alse of the larger end are broad and diverge towards the middle of the chela, and 

 their sides are much refolded. The tooth is rather narrow, and most frequently somewhat rounded at 

 the end; the tuberculum is long and narrow, and there is a rather broad falx. The alse of the smaller 

 end are broad, and diverge only a little towards the middle of the chela, and their sides are much 

 refolded; the tooth is rather broad, and the end is straightly cut off, the tuberculum is small and 

 elliptic. Both alse and tooth here being broad they leave only a narrow slit between them. While the 

 alse and the tooth of the larger end converge towards the end of the chela, this is only to a slight 

 degree the case with those of the smaller end, and consequently this end gets a peculiar, straightly cut 

 off appearance. Both the alse and the tooth in the smaller end of the chela are curved about in a 

 circular line, so that a transverse section through the chela would here be almost a circle. These 



