-, PORIFERA. I. 



1^ 



and o-ive to the surface its shaggy appearance'). In the meshes of the reticulation numerous round 

 or most frequently oval pores are found, measured to a size of 0-017 — 0119'"'". In the dermal mem- 

 brane sigmata of the common form are copiously found. 



The skeleton^ as stated by Ridley and Dendy, consists of an irregular reticulation of poly- 

 spicular fibres; especially the fibres running towards the surface (the primary ones) are distinct, while 

 the others are indistinct, lying irregularly, or dissolved into single spicules. The primary fibres have 

 an average reciprocal distance of the length of one spicule. The number of spicules in the primary- 

 fibres ma>- be somewhat var)-ing, but most frequently it appears to be 4 — 6. As mentioned, a coarse 

 and irregular reticulation is seen under the skin, and this reticulation is accordingly formed by second- 

 ar\- fibres, but in the nodes the ends of the primar\- fibres project making the surface slightly shaggy. 

 Spongiu uniting the spicules is found, but to a rather slight degree; besides it is clear, and therefore 

 not easily observable. 



Spicula: a. Mcgnsclrra are oxea, slightly and evenly curved, more rarely with a somewhat 

 sharper curve, with evenly, but not long tapering ends. The length is rather constant 0-416 — 0-447™""; 

 only rarely it goes down to 0-38'""', or rises to 0-476""™; also the thickness is rather constant, and is 

 between o-oi6 and 0-012"""°. Shorter and finer spicules are found in very small numbers, b. Micro- 

 self ra : I. Sigmata of the common form; these sigmata have a regular form, they are rather varying 

 in length, from 0-02 — 0-07'""""; the latter size, however, is only rarely attained, the average size being 

 about 0-04'"'""; the)- are rather fine and have an average thickness in the middle of ca. 0-0018"""""; the 

 greatest ones may reach a thickness of up to 0-0026"°"". These sigmata are frequent throughout the 

 sponge, and occur in especialh- large numbers in the dermal membrane. 2. Flagellate sigmata; these 

 sigmata are long ones, so highly curved in the middle as to get two more or less parallel arms; the 

 ends are evenly pointed, and are bent inward in an almost rectangular or acute-angled way and with 

 a rather sharp curve; most frequently, but not in all instances, one arm is somewhat longer than the 

 other, and the short arm has the largest hook. With regard to the size, the greater axis of the sigma 

 is 0-078—0-09"°'"", and the smaller axis about 0-057°""". The thickness is between 0-0028—0-0035'""". These 

 sigmata are rather numerous througli the whole sponge, although not so numerous as the small ones, 

 and they are not found in the dermal membrane. 



The flagellate sigma of my specimen shows a little difference from the figure in Ridley and 

 Dend)-; this difference, however, con.sists only in the fact that the hook of the short arm has not in 

 the figure of Ridley and Dendy the sharp curve described by me; there is, however, no reason to 

 put au)- stress upon this fact, as these sigmata upon the whole are somewhat varying in form, and 

 Ridley and Dendv have onlv figured a single individual. The measures of these authors agree 

 with my measures, when we notice the fact that they give the length from the shortest arm to the 

 curve; a remeasuring of their figure gives the length of 0-08™"" for the greater axis. 



Of the small sigmata the said authors say: possibly young forms of the others ; this opinion 

 is a consequence of the way in which they explain the growth of the chelse, since they, with regard 

 to these spicules, also interpret the small forms as developmental phases of the larger ones. In order 



I) Ridley and Dendy say: (Surface .... slightly rough, probably owing to the dermal membrane having been 

 in most parts rubbed off.. The surface, however, as will appear from the description above, is also shaggy when undamaged. 



