EEPORT ON THE HEXACTINELLIDA. 8 



a prolonged period, for purposes of comparison, portions of most of the Hexactinellida 

 which he has described, and also a very large nuniber of microscopical preparations. 

 From Dr. Marshall of Leipzig I likewise obtained the use of portions and preparations 

 of all the specimens which formed the basis of his own Hexactinellidan ol)servations. 

 I have been similarly assisted by Hofrath Director A. B. Meyer of Dresden, 

 Professor Semper of Wiirzburg, Professor von Martens of Berlin, and Professor Moseley 

 of Oxford. In the important work of determining forms, a visit which I paid to London 

 was of much value, since, through the Challenger Expedition Commission, I was enabled 

 to study the original specimens of several Hexactinellida described by Owen, Gray, 

 Bowerbank, Carter, and others. During my work in London, not only were the rich 

 treasures of the Museum made accessible to me in the most liberal way by Dr. Giinther, 

 Director of the Zoological Department of the British Museum, but I was also accommo- 

 dated with a private work-room in the new building of the British Museum in South 

 Kensington. There I enjoyed the most attentive and friendly assistance of Mr. 

 S. 0. Ridley. 



I had valuable assistance of another kind from Dr. Vosmaer of Naples, who had the 

 great kindness to place at my disposal the manuscript of that portion of his great 

 Spongiological Bibliography (in course of ^preparation) which dealt with the 

 Hexactinellida. 



In the preparation of the numerous plates I have been ably helped by my assistant, 

 Dr. von Miihrenthal, who has photographed a number of objects, and by Mr. G. 

 Firtsch, one of my students, who has executed numerous drawings from my sketches 

 and according to my directions. 



It is my pleasant duty to return "my best thanks to all the gentlemen whom I have 

 named, but especially to the Director of the Challenger Office, Mr. John Murray. 



With regard to the figures given in the plates, I have still to note the following 

 points. From the scientific papers belonging to Sir Wyville Thomson, sixteen 

 lithographed plates have been handed over to me, all of which have been incorporated 

 in the present work, viz.. Pis. I., 11. , V., VIL, VIII., IX., X., XV., XXXI. , XXXV., 

 XL., XLV., XLVL, LI., LXVL, and LXVII. As these had not yet been printed ofi" 

 when I received them, I was able to make several corrections, though I have pre- 

 ferred to leave most of them unaltered. Only from Pis. XXXI. and LXVII. a 

 few figures have been removed, which represented spicules not really belonging to the 

 Sponges figured. Every authority will admire the beautiful and life-like figures both 

 of the entire Sponges and of the separate preparations which are found in Sir WyviUe 

 Thomson's plates. I was not able, however, to follow the method illustrated in these 

 plates, since I could not confine myself merely to the general form of the Sponge, nor to 

 the structure of the skeletal elements, but had also to give representations of the soft 

 parts. It seemed to me, further, especially desirable to display the internal architecture 



