INVERTEBRATA , CRYPTOGAMIA, MICROSCOPY, ETC. 103 



substance sand-grains and other foreign particles adhering to the 

 connli, or elevations of the surface into which the ends of the chief 

 fibres project. 



The collar-cells (endoderm) resemble those of other horny sponges : 

 they are usually elongated and cylindrical, with a rounded nucleus at 

 the base. They form a single layer, lining the hemispherical ciliated 

 chambers, each of which has usually four or more inhalent pores and 

 a large exhalent canal. 



The ova, as in other sponges, arise as irregular roundish cells in 

 the hyaline ground-substance of the connective layer. The ripe eggs 

 are oval, • 25 mm. in diameter, with granular yolk and a large germinal 

 vesicle with germinal spots. It was made out that, as the egg 

 became ripe, the germinal vesicle approached the periphery, and com- 

 pletely lost its vesicular character, appearing merely as a bright 

 speck. 



One important point is that, in this genus, the eggs are not 

 irregularly scattered through the mesoderm, as in other sponges, but 

 occui- in definite groups of ten to thirty, embedded in gelatinous con- 

 nective stroma, and forming together a globular mass, which may 

 be taken as the first appearance of an ovary. The period of sexual 

 maturity is independent of the time of year. 



Sperm aggregations were only found in one specimen, which 

 contained no eggs, so that probably the sexes are distinct. 



Yolk-division is regular and symmetrical : no cleavage cavity was 

 to be seen. The oldest larva examined was somewhat elongated, convex 

 at one pole, slightly excavated at the other, and consisted of a 

 central mass of parenchyma-like cells, surrounded by a single layer of 

 very small, cylindrical, ciliated cells. Pigment occurred in the outer 

 layer, both at the convex pole and in the raised rim surrounding the 

 depression at the opposite extremity.* 



Cacospongia. — The paper concludes with a description of three 

 species of this genus, which does not differ in any important par- 

 ticulars from Eus^wngia. 



Histology and Gemmation of the Tethyae.f — In addition to the 

 following results. Dr. Bcla Deszo he gives valuable hints as to 

 methods for the study of these difficult organisms. 



The cells — c. g. of the syncytium — were brought out by Bcale's 

 carmine. The gommco were studied by thin hand-made sections after 

 treatment with ^ per cent, perosmic acid and with ammonia-frco 

 carmine. By these means a very considerable complexity of histo- 

 logical arrangement is demonstrated to exist in Tethya lyncurium, 

 which was the special form selected for study. 



A distinct epithelium, consisting of a single layer of flattened cells, 

 covers the outer surface of both the gemmro and adult ; in the former 

 case they are oval in sliajie, in the adult they are polygonal and smaller. 



An endothelium clothes the interior of tlie water-passages, and 

 difiers from the epithelium in the more massive shape of its con- 

 stituent colls. 



I * Cf. MetBchnikoff, tbis Journal, ii. (1879) p. 874. 

 t ' Arch. Mikr. Aniit..' xvi. (1879) p. 62U. 



