404 On the Anatomy and Embryology of the Phalangiidae. 



sjiinnlng-glands'of Pertpatus and the setse-forrning glands of 

 the Annelids j)roves to be untenable. 



10. The ccphalothoracic glands described by Krohn are 

 constituted in the final stages of development as two pyriforin 

 invaginations of the ectoderm at the side of the two eyes 

 (figs. 40, 41, and 47, c. dr.). In the ectoderm cells of the 

 glands there commences at an early period the secretion and 

 accumulation of a dark pigment which forms two black 

 spots upon the surface of the embryo, which is still perfectly 

 white ; these spots are visible like the eyes through the f^'^^- 

 membvanes. Simultaneously with the glandular structures 

 which have been described there exists in the embryo a pair 

 of provisional organs of a glandular character. In Gerastoma 

 cornutum these appear as two groups of large cells^ lying 

 one on each side in the cephalothorax near the eyes. Exter- 

 nally these cells are directly covered by the ectoderm, and 

 they appear to be separated from the body-cavity by a thin 

 memhr ana propria. In addition to a large nucleus the cells 

 of this organ enclose peculiar concretions, which take a deep 

 stain from carmine. Although covered by the ectoderm these 

 cells nevertheless possess a communication with the outer 

 world by means of a special aperture, through which the 

 concretions which are formed in them are conveyed to the 

 exterior. In the sections a compact mass of these excretions 

 generally lies at this aperture (figs. 39, 40, 41, 44, and 45). 

 In another undetermined species of Phalangium the glandular 

 structure of this organ was even more pronounced. In this 

 case it consisted of a tolerably large hemispherical complex 

 of cells, which projected freely into the body-cavity and was 

 attached to the ectoderm by a relatively smaller portion 

 (figs. 42, 43, 46, and 47) ; the apices of the columnar and 

 distinctly defined pyramidal cells of this organ met together 

 in a point, while their broad bases formed a hemispherical 

 surface. In each cell a large nucleus was situated not far 

 from the base, while the excretory products were accumulated 

 nearer the apex. The external aperture of the gland had the 

 form of a small pit, filled with secretion deeply stained by 

 carmine; short rods of this secretion radiated from this ])it 

 between the apices of the cells (fig. 43). But these glands 

 had not exactly the same structure in all preparations of this 

 species of Phalangium] in some cases they were suggestive 

 of those of Cerastoma cornutum (fig. 48). At the same time 

 the embryos investigated were all at the same stage of deve- 

 lopment. I have consequently found in two species of Phalan- 

 gium during embryonic development a peculiar glandular 

 organ, which lies in a single pair in the cephalothorax, 



