Prof. M. Schultze on Hyalonema. 155 



I have rauged the polypes under the genus Palythoa, and think 

 that in so doing I was nearly right. According to Professor 

 Oscar Schmidt, there occurs in the Adriatic a perfectly similar 

 polype, which he likewise refers to the genus Palythoa^ and which 

 also occurs only as a parasite upon a sponge. Two species of 

 the genus Axinella are always covered with this parasite, which, 

 moreover, was found upon no other sponge, nor upon any other 

 foreign body in the Adriatic Sea (0. Schmidt, Pie Spongien des 

 Adriatischen Meeres : Leipzig, 1862, p. 61, taf. vi. figs. 2, 3). 

 In this we have the most perfect analogy to the parasitism of 

 Palythoa fatua upon Hyalonema] and it is well known that many 

 such examples of exclusive parasitism upon a particular host 

 occur in nature. 



If, therefore, it is indubitably established that the long threads 

 of the " Glass Rope '' are sponge-spicules, the occurrence of a 

 sponge-body at one of its ends, as already mentioned, acquires 

 peculiar significance. This sponge, in the specimens in which 

 it is completely retained (as, for example, in several of those 

 figured by me from the Ley den Museum), presents a pyriform 

 body, which so completely envelopes the lower extremity of the 

 " Glass Rope '' that nothing can be seen of the latter. The broad 

 base of the sponge is directed downwards, the cord of long siliceous 

 threads projecting freely from the middle of the superior narrowed 

 extremity. The sponge itself consists of an elegant tissue of 

 dense masses of very short siliceous spicules. 



If the sponge be opened by breaking through the dense felt 

 of fine siliceous spicules, the long siliceous threads are found to 

 terminate in extremely fine ends in the axis of the sponge, and 

 to be united in a very characteristic manner with the tissue of 

 the latter (see taf. ii. fig. 1 of my monograph) . No one who 

 has performed such a dissection can doubt that the most inti- 

 mate organic union exists between the porous sponge and the 

 " Glass Rope,^' and that both, therefore, form an organic whole. 



But in many specimens in collections the sponge is wanting, 

 and the siliceous threads terminate freely at both ends. I have 

 submitted a great number of such specimens, in which the sponge 

 was deficient, to a careful examination, and found that whenever 

 the lower attenuated extremities of the siliceous threads were pre- 

 served these were always united to each other by distinct remains 

 of a sponge-tissue. The microscopic examination of this always 

 revealed a complete agreement of its spicules with those of the 

 sponge-body of the perfect specimens above described. Thus, 

 as I could almost always detect very characteristic traces of the 

 sponge even in my imperfect specimens, injured in many ways 

 by mechanical violence, and, indeed, in those which had been 

 wedged with stones into the borings of Pholades, I do not hesitate 



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