PORIFERA. II. 



H3 



Tension spicula acuate*, whereas, in the description and in the third volume under the explanation 

 of the figures, he speaks of the spicules of the dermal membrane as monactinal ones. b. Microsclera; 

 these are tridentate isancorae spatuliferse of two sizes, i. The large ancorae have a somewhat curved 

 shaft, the teeth are oval and more or less broadly rounded at the end, sometimes pointed. The shaft has 

 distinct alas, a trifle longer than the teeth. The free part of the shaft between the alse is about one 

 fifth of the length. The ancora may vary somewhat in form, be more slender or more robust, and 

 the tooth may vary a little in breadth. The length varies from 0-064— 0-09™ m , m by Iar most cases 

 it is midway between the two sizes; the thickness of the shaft is 0-0057— o-oo8 mm . 2 - The small 

 ancora: have a similar form as that of the larger ones, the only difference being that the teeth of 

 the two ends approach considerably in the middle. Their length varies from 0-022— 003 5 mra , and the 

 thickness of the shaft is 0-0021—0-0028. Developmental forms in different stages are found of both 

 forms of ancorse, from exceedingly fine ones with only slight traces of teeth. Transitional forms 

 between the two forms of ancorse have not been observed in this species. Both forms occur in the 

 dermal membrane and in the membrane-like parts of the sponge, often in large numbers; the small 

 ancora is the more frequent one. 



Embryos. In some of the individuals embryos were found copiously in the tissue. They are 

 globular, the largest ones of a diameter of ca. o-3 mm . The smaller ones had no spicules, then mega- 

 sclera occurred, and the larger ones showed both megasclera and developmental forms of the small 

 ancora. The megasclera are spined tylostyli reaching a length of up to o-i4 mm and a thickness below 

 the head of up to o-oo4 mm . The developmental forms of the ancora were of the same length as in the 

 grown sponge. At first the megasclera occur in small numbers and scattered; later, at the same time 

 as they grow larger, they are numerous and closely gathered in a bundle; they are, especially at the 

 head-end, far more coarsely spined than in the developed sponge. In the largest embryos the small 

 ancora was fully or almost fully developed. The specimens in question were obtained in the mouths 

 of May and July. 



By comparison with a specimen of M. fimbriate/. Bow. sent me by the Rev. Mr. Norman I 

 have been able to identify the species with certainty. From incrustans it is separated, besides by other 

 characters, by the absence of sigmata; otherwise it is well characterized by its round or round-lobed 

 form, its even surface, and the solid, not thin dermal membrane. 



Locality: The species has been taken by the Ingolf, station 32, 66° 35' Lat N., 56 38' Long. W. 

 depth 318 fathoms; station 85, 63 21' Lat. N., 25° 11' Long. W., depth 170 fathoms; station 89, 64 45' 

 Lat. N., 27° 20' Long. W., depth 310 fathoms; station 98, 65 38' Lat. N., 26 27' Long. W., depth 138 

 fathoms; station 127, 66° 33' Lat. N., 20° 05' Long. W., depth 44 fathoms. It has further been taken at 

 the following localities: Iceland, Cape North, depth ca. ^ fathoms (Ditlevsen); 64 27 Lat. N., 13 3 27' 

 Long. W., depth 84 fathoms, 6o c 55' Lat. N., 8° 56' Long. W., depth 69 fathoms, 62 23' Lat. N, 2 35' 

 Long. E., depth 217 fathoms (Ad. Jensen, the cruise of the Michael Sars> 1902); the Faroe Islands, at 

 the south end of Nolso, depth ca. 80 fathoms, at the north end of Nolso, depth ca. 100 fathoms, 9 miles 

 east of Nolso, depth ca. 30 fathoms, 6 miles north to west of Kalso, depth 60 fathoms, 8 miles south- 

 east of Miavenass, depth 40 fathoms, off the mouth of Borovig, depth ca. 30 fathoms (Th. Mortensen) ; 

 southwest of Myggenaes, depth 135 fathoms (Ditlevsen). Altogether about twenty larger and smaller 



