164 



GEODIA OVIS. 



The large amphioxes (Plate 40, figs. 6-13, 27; Plate 42, fig. 2b) are slightly 

 curved, not very sharply pointed, 4-9, mostly 7-8 mm. long, and in the middle 

 30-100 fjL, the long ones 70-100 /x thick. Their terminal parts (Plate 40, fig. 27) 

 are more rapidly attenuated towards the ends than is the central part. The 

 two ends are usually slightly unequal. Two of these amphioxes measured: — 







A 



B 





100 /( 



from one end 



20 



23 



/( in thickness 



200 /( 





31 



31 



/' " 



300 /( 



tl U (( 



39 



35 



/' " " 



in the 



middle 



76 



72 



u " 



300 /( 



from the other end 



32 



37 



n " 



200 /( 



(1 i( 11 n 



29 



30 



/' " 



100 /( 



ti il H tl 



19 



21 



/' " 



The rare large styles and tylosiyles are of two different kinds. The one kind is 

 short and stout, the other very long and slender. Those of the former are 

 probably amphiox-derivates, those of the latter perhaps anaclade-derivates. 

 The short and stout ones are true styles, or, if tyle, only slightly thickened at 

 the rounded end, the tyle exceeding the adjacent parts of the spicule not more 

 than 10 % in transverse diameter. These styles (tylostyles) are 2.6-4 mm. 

 long; the rounded end (tyle) is 85-116 /i thick. The long and slender spicules 

 of the latter kind are all tylostyles. Their length is considerable, but could not 

 be exactly ascertained because all I observed were broken off. These spicules 

 are about 40 pt thick; their elongated, oval tyle measures 60-65 jj. in trans- 

 verse diameter. 



The minute rhahds (Plate 42, figs. 3a, 4-7, 24a), which form the dermal 

 tufts and also occur scattered in the choanosome, are mostly amphioxes. Many 

 of them are distinctly anisoactine, and in some one end is rounded off. The 

 latter appear as styles. These minute rhabds are much more variable in length 

 than in thickness. They are 270-440 fi, occasionally as much as 550 /i, long or 

 even longer, and 8-13 /« thick. 



In the minute dermal rhabds of several geodine sponges, and particularly 

 frequently in those of the species under consideration, I have noticed a remark- 

 able anisoactinity of the axial thread (axial canal), this being very much thicker 

 (wider) at one end than at the other. One half of the axial thread (canal) is 

 in these spicules normally developed and appears as a thin, cylindrical thread. 

 The other half increases in thickness (width) from the centre of the spicule to 

 the end in a funnel-shaped manner. The end of the spicule in which this dis- 

 tally widened half of the axial thread (canal) terminates, appears as a thin- 

 walled tube. In the style-rhabds it is always the pointed end which contains 



