ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 383 



the female, and are at this time 18 to 19 /a in diameter, spherical in 

 form, having their protoplasm filled with refractive granules, which call 

 to mind the vitelline granules, and they have a nucleus which is easily 

 stained. In the female organs the refractive or nutrient granules 

 diminish gradually and finally disappear. The deutospermatoblasts 

 now present the most varied forms, and look more like Amcehce. It 

 is at this time they become spermatozoa, the substance of which is 

 formed from the interior of the cells, and appears first as a differen- 

 tiation of the protoplasm, and surrounded by a delicate granular layer 

 — the remains of the deutospermatoblast ; it is remarkable that the 

 deutospermatoblast is constantly outside the spermatozoon. This 

 latter has at first the form of a rounded cylinder, but its surface 

 rapidly becomes spiral and one end enlarges as the other diminishes. 

 At the moment of fecundation the ovum is surrounded by a finely 

 striated zone, to which the conical spermatozoon becomes attached 

 by its base ; the yolk contracts slowly, the spermatozoon enters, but 

 there is apparently no micropyle ; the peripheral part of the yolk 

 forms a granular zone which surrounds the male element, part of 

 which advances as a fusiform male pronucleus to fuse with the female 

 pronucleus. The yolk again contracts and a polar globule is formed. 



Structure of Derostoma Benedeni.* — P. Francotte, after an histo- 

 rical review of the characters of the genus Derostoma and its 

 rhabdoccBlous allies, gives a short diagnosis of the new species he has 

 discovered at Andenne, where it was found in a stream, in the midst 

 of a number of Tubifex rivulorum on which it feeds. In the ante- 

 rior part of the body the epithelial cells are higher than elsewhere, 

 their cilia are longer, and between the cells the ends of nerve-fibres 

 could be detected, though their exact relations were not made out. 

 The pharyngeal bulb is largely formed of muscular fibres, and is 

 moved by a set of thick fibres which are attached to its dorsal and 

 ventral surfaces and so produce movement in all directions. The 

 muscular fibres in all parts of the body are smooth and non- 

 nucleated ; they appear to be formed of a large number of delicate 

 fibrils. 



When a specimen has been rendered transparent it is possible to 

 see, in the anterior region, two ganglia united by a transverse com- 

 missure ; each of these ganglia gives off two nerves which pass to 

 the epithelium, and two others which are longer and pass backwards 

 to innervate the various organs of the body ; on the ventral surface 

 of the worm there is yet another pair of nerves. The two ganglia 

 and the commissure are formed externally by ganglionic cells, while 

 the centre is filled with nerve-fibrils ; on the course of the nerves 

 large nerve-cells, similar to those of the central nervous system, are 

 not rarely met with. The cells which line the digestive tract are 

 stated to be globular during digestion, and to be elongated in sections 

 made from fasting specimens. 



The penis is not, as in some species, chitinous, but is formed of 

 muscular fibres. Between the ovary and the receptaculum seminis 



* Bull. Acad. R. Belg., vi. (1883) pp. 723-35 (1 pi.). 



