ON THE OCCURRENCE OF l'HOUONIS AUSTRAEIS NEAR MISAK1. 117 



the host derives any advantage from the presence of the commensal 

 worms. 



These are found, usually close together in a large number, near tha 

 upper end of the Gerianthus tube. The greater part of the body, covered 

 by ils own, loosely fitting, chitinous tube, lies imbedded in the 

 gelatinous tube of the host in such a way that the posterior worm-end 

 which is free from that of the neighbors, is directed downwards and 

 somewhat obliquely outwards, while the anterior slender portion with 

 the tentacular crown projects into the lumen of the host-tube, and thencü 

 outwards through the opening of the same 



The worm may reach 90 mm. in total length and 4 mm. in breadth 

 at the broadest part. The tentacles are 12 — 15mm. long ; they are 

 arranged in two and a half double coils on each side. That part of the 

 body which lies within the tuba-wall of the host is of a pink color, while 

 the remaining parts are, as already indicated, deep reddish brown. 



Closely behind the aboral lophophoral cleft are situated the anal 

 ridge and the nephridial ridges, both showing the same characteristic 

 features as were described by Benham. Over these ridges, as in fact 

 over the entire deeply pigmented portion of the body proper, the skin in 

 the fresh state exhibits closely set circular wrinkles. 



The lophophoral chamber contains segmenting eggs and different 

 developmental stages reaching up to such larvae a.s are in possession of 

 four pairs of tentacles. These larvae are of a moderately large size, being 

 on the whole relatively thick and short. The anal ciliated belt is dis- 

 proportionately large; the collar and the tsntacular bases are shaded 

 with reddish brown pigments. In a few casss examined of free-swimm- 

 ing larvae, evidently belonging to the species and which were obtained 

 by means of a surface-net in the neighbourhood of the spot inhabited by 

 the mother-animals, I hive found the number of tentacles increased to 

 8 — 10 pairs ; in other respects they were strictly comparable to those still 

 contained in the lophophoral chamber. And, in these peculiar larvae 

 found at large, I recognize a form which, long before the mother-animal 

 became known to me, once came under my observation in a hm : ted 



