REPORT ON THE CALCAREA. 11 



denying the possibility of establishing the homology of the Ascon with the radial 

 tube. M. Barrois l also, supported by facts drawn from the domain of embryology, re- 

 marked the great affinity between Sycones and Leucones, not Ascones ; but it is the merit 

 of Dr. Vosmaer 2 to have submitted the question to a detailed and critical examination. 



Belying upon the observations of F. E. Schulze and Barrois, as well as upon his own 

 anatomical researches into Leucandra aspera, H., Vosmaer urges that the radial tubes 

 are nothing but a kind of flagellated chambers ; he refutes the strobiloid gemmation 

 hypothesis, on the ground of the difference in the disposition of the spicules in the radial 

 tubes and in the walls of an Ascon, which had been already made out by Brof. Schulze, 

 and which can be really regarded as a decisive proof against Hseckel's speculative 

 hypothesis. As a second argument against it, he compares the disposition of the anchor- 

 like spicules in Sycandra raphanus and in Syculmis synapta — an observation also due 

 to Brof. F. E. Schulze, but, as Barrois had already shown, 3 hardly possessing any 

 phylogenetic value. Finally, Vosmaer develops his own views as to the phylogenetic 

 affinities of the three families of Calcarea ; and I here emote the most important passages 

 with some abbreviations : — 



" The Ascones present the simplest form of the canal system. The thin wall of the 

 sponge consists of three parallel layers, ectoderm, mesoderm, and endoderm. Here and 

 there the cells separate, and thus give origin to the pores (Hreckel's ' Lochcanale '). The 

 water, flowing along the outer surface, enters through the pores into the interior, and 

 washing the endodermic cells runs out through the osculum. Now, it is evidently 

 advantageous to the sponge, that the surface washed by the water be extensive. One may 

 consequently well imagine any increase in the surface to be a favourable factor in the 

 struggle for existence. If in an Ascon such an extension of the surface, particularly of 

 the layer of the flagellated cells (' in's Besondere der Kragenzellenschicht ') take place, the 

 layer just named will form folds and invaginations. Let us suppose that in such a 

 manner small lateral pouches are formed, and again that these pockets grow larger and 

 develop along the whole wall regularly ; it is evident that we have before us the picture 

 of a primitive Sycon. All this is quite in harmony with the facts of embryology. Hseckei, 

 Barrois, Schulze, and others, have shown that an Olynthus-phase is passed through in the 

 development of the Sycon, and yet Olynthus is nothing but a primitive Ascon. Lieber- 

 kiihn had previously observed that the radial tubes are only invaginations of the gastric 

 wall, and that the wall of the radial tubes is covered with flagellated epithelium, which is 

 wanting on the gastric wall of the sponge. That this latter is covered with pavement- 

 cells, Lieberktihn did not know ; nor Hseckel either. Schulze first discovered it in the 

 year 1875." 4 



1 Embryologic de quelques eponges de la Manche, Ann. d. Sri. Nat, s£r. G (Zool.) t. iii. art. 11, p. 52, 1876. 

 - Ueber Leucandra aspera, Tijdtchr. d. Ned. DUrk. Vereen. Dl. v., p. 156, 1831. 

 3 Loc. cit., p. 31. * Loc cit., pp. 156, 157. 



