10 THE VOYAGE OF II.M.S. CHALLENGER 



contact with each other and anastomose, thus forming still larger sinus-like spaces." 1 

 This modification in, according to Hseckel, rare; it is to be found in Leucilla amphora, 

 Leuculmis echinus, Leueandra Jistulosa, Leucandra cucumis, Leucetta corticata, and 

 Leucaltis clathria; in the two latter forms, however, it is not so well-marked. 2 The 

 corresponding diagram refers to Leucandra Jistulosa. The only specimen of this form I was 

 able to obtain proved to be so badly preserved that there was nothing to be seen in the 

 sections but spicules. There were, however, in the Challenger collection, some specimens 

 which compensated me — at least in some degree — for this mischance. In Leucilla uter, 

 n. sp., I found a form closely allied to Leucilla amphora; on the other hand, 

 Leucetta vera, n. sp., and Leucetta hceckeliana, n. sp„ show such an unmistakably intimate 

 relationship to Leucaltis clathria, that there are just differences enough to separate 

 these forms into distinct species. 



The corresponding illustrations are given in PL VI. fig. 2a, and PL Till. figs. 1 and 

 7. In the for-ms just mentioned I could discern neither the network of ramifying 

 canals in Hasckel's sense, nor the fusion of the flagellated chambers, the structure of their 

 canal system quite corresponding in its chief characters with that of all other Leucones. 

 However, in one case (Leucilla uter) I found the flagellated chambers not to be round, but 

 of an elongated, cylindrical form, and also of much larger dimensions than usual ; and in 

 another case (Leucetta vera) there were the smaller, more roundish chambers in addition 

 to the cylindrical ones. I fancy that Prof. Hseckel must have seen something of this 

 kind, and that it was just the difference in the size of the flagellated chambers which 

 gave him the idea of a vesicular type of canal system. I think also that Prof. 

 Haackel must have had to deal with very badly -preserved specimens, and thus, having had 

 no other guide but his phylogenetic speculations, came to conclusions which, seen from a 

 modern point of view, sometimes appear rather singular. 



I might now pass on to the question which has necessitated this digression, viz., the 

 systematic value of the properties of the canal system, but that can be answered thoroughly 

 only w T hen we have acquired a perfectly clear conception as to the phylogenetic relations 

 subsisting between the three families of Calcarea. 



As I remarked before, Prof. Haeckel considers the Sycon to be equivalent to a colony 

 of Ascones, which has originated by means of a strobiloid gemmation. According to him, 

 every radial tube of the Sycon is the homologue of a whole Ascon, its conjectural dermal 

 ostium a homologue of the osculum, its pores of the pores perforating the wall of an 

 Ascon (comp. Sycetta primitiva, Kalkschwanime, Bd. hi. pi. xli.). Now, the case is quite 

 different with regard to the Leucones. According to Hgeckel, the Leucon is nothing but 

 an Ascon whose walls have grown thick and whose pores have changed into canals 3 



Prof. F. E. Schulze i was the first to pronounce an opinion upon this subject, 



1 Kalks.-lnvamme, Bd. i. p. 234. 2 Kalkschwiinime, Bd. i. p. 235. 



3 Kalksekwamme, Bd. i. p. :;17. « Zeitschr. f. iciss. Z00L, Bd. xxv., Suppl, p. 225, 1875. 



