IO PORIFERA. III. 



to strongyles. They are more or less curved, but rather slightly; the shaft is thickest at the middle 

 and tapers somewhat towards the ends. The spicules vary very much in size, and at the same time 

 somewhat in shape; the smaller and thinner they are, the more distinct are the end-swellings; 

 these smaller spicules have equal or nearly equal ends; the larger and thicker the spicules are, the 

 smaller are relatively the end-swellings, so that in the largest of the spicules they may be onlv 

 slightly pronounced; in the largest spicules the ends are most often not equal, one has a somewhat 

 roundish swelling the other an elongated swelling tapering slightly outwards; not rarely the 

 swellings quite disappear, and then we get a strongyle with unequal ends, one rounded the other 

 more tapering, nearly truncately pointed. The various sizes must be taken to be fully developed 

 spicules, since fine developmental stages in various lengths are found; the developmental stages have 

 unequal ends, the shaft being a little thicker in one end but a little thinner in the other, and here 

 with a more marked swelling. Quite single very fine developmental stages were found, which had one 

 end quite pointed. The length of the spicules is in all 0*27— o - 95 mm , with a diameter of 0-005 — o - 02i mm . 

 The length of the spicules is different in the different parts of the sponge; in the dermal layer the 

 largest are found, while the smaller and smallest are found in the inner body, the separation is how- 

 ever not quite sharp. In the inner body they generally do not exceed o-6o mm , and about at the same 

 size also lies the lower limit for the spicules of the dermal layer. In the skeleton of the fistulae large 

 and small spicules are mingled. In the fibres running along the surface of the inner body the 

 spicules belong for the most part to the larger forms of the group with the smaller spicules, and 

 among them some of the largest spicules are found, and with this composition the fibres continue out 

 through the fistulae. Carter mentions and figures two forms of megasclera; to this result he arrives 

 only by taking a pronounced tylote and a form without end-swellings, and in which one end is truncately 

 pointed ; a form such as his figure 39 a may be found, but not frequently, and there is, as said, only 

 one kind of megasclera. b. Microsclera ; there are two forms, chelae arcuatse and sigmata. 1. The 

 chelae arcuatae have an evenly curved shaft, lobe-shaped alae and an elliptical tooth; their length 

 is 0-040— 0-046 mm and the diameter of the shaft is 0-004 mm . 2 - The sigmata are of common shape 

 and more or less contorted; they are rather large, but they vary somewhat in size, the length is 

 0-047 — °'°93 Inm an d the thickness 0-0028 — 0-0057 m,n . The microsclera are present through the whole 

 sponge, they are scattered in the inner body and in the dermal layer strewn rather numerously 

 among the megascleres, and they are specially numerous on the inside of the fistula;; the sigmates 

 are everywhere more numerous than the chelae. 



Embryos. In one of the specimens which was cut through an embryo was found, lying in a 

 cavity in the inner body. It was globular and rather large, 3' nm in diameter. It was lying in the 

 cavity distinctly surrounded by a membrane. It was richly provided with spicules, both megasclera 

 and microsclera. The megasclera were fine tylotes of a greatest length of about o - 47 mm , many of them 

 were very thin and had still one end pointed. They were scattered in the interior of the embryo, 

 but they were already close-lying at the surface and parallel to this, thus forming a layer with how- 

 ever no boundary inwards. The microsclera were developmental forms of chelae in various stages, 

 they were of somewhat different sizes, but reached a length of up to 0-057 mm , tnus to a greater size 

 than in the fully developed sponge. Sigmates were not seen. 



