ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 611 



Lencandra aspera and the Canal System of Sponges.* — G. C. J. 

 Vosmaer, in studying the Leucones, has come to somewhat different 

 conclusions from those of Haeckel and Keller with regard to their canal 

 system. His conclusions are based chiefly on the above-mentioned 

 species. With regard to its canal system, it may be seen with a lens that 

 the outer side of the sponge is beset with numerous small openings, 

 while those of the gastral face are considerably fewer but larger. 

 Sections made of alcoholic specimens (after decalcification with crude 

 wood-vinegar) in the horizontal, vertical, and tangential directions show 

 that the inhalent orifices lead into comparatively wide canals, which 

 penetrate the body-wall either directly, or by branching, or by anas- 

 tomosing together ; the gastral openings, too, lead into wide canals, 

 and the two sets of canals are connected by the ciliated chambers. 

 These chambers open directly into the wide excretory canals, but 

 communicate with the inhalent tubes only by small pores (" chamber 

 pores"). The ciliated chambers lie radially around the excretory 

 canals, mostly close together. This arrangement of the canal system 

 agrees with that of Aplysilla, Spongelia, and other forms. Three 

 regions may be distinguished in the wall — an outer, spicular one, 

 containing triradiate and linear spicules ; a median one, with the 

 ciliated chambers ; and an inner spicular one, containing chiefly tri- 

 and quadri-radiate forms. As Schmidt and Keller have stated, the 

 quadriradiates sometimes disappear altogether. 



Histology. — Yosmaer finds three histologically distinct body- 

 layers, but withholds his judgment as to their relation to embryonic 

 conditions. The first layer (a) is the tabular epithelium, which 

 in L. aspera covers all the surfaces, internal and external, with 

 the exception of that of the ciliated chambers, and extends over the 

 bases of the large projecting linear spicules. It exhibits practically 

 the same characters in all parts, though in the so-called entoderm the 

 cells are somewhat smaller than elsewhere. The cells are large, flat, 

 sometimes bearing long processes, quadrangular or polygonal in out- 

 line, with a coarsely granular protoplasm, which is only slightly 

 coloured by h8Bmatoxylin ; they have a finely granular, round nucleus, 

 with one or more nucleoli. It is probable, but not certain, that a 

 cuticle covers and unites the cells; they are separated by clear 

 spaces. (&) The second layer is formed by the connective tissue and 

 its products, derived most probably from the mesoderm ; that it is of 

 the nature of connective tissue, and not a Syncytium, in which the 

 nuclei are the only distinctive traces left of the original cells, now 

 fused together, seems to the author more in accordance with the fact 

 of its composition of fusiform or stellate cells with distinct nuclei, 

 with its often firm consistency, with the results of Metschnikoft^'s 

 experiments with acids, with the slight capability for becoming stained 

 which the ground-substance possesses, and finally, with the generally 

 admitted connective-tissue nature of the closely similar tissues, 

 embryonic connective tissue, Medusan gelatinous tissue, Cephalopod 

 cartilage, the mantle of Tunicates, &c. In this particular sponge, 

 this layer consists of a completely hyaline ground-substance inter- 



* Tijd. Ncderlaud. Dierk. Vereen., v. (ISSl) pp. 144-64 (2 pis.). 



