JOURNAL OF MICROSCOPICAL SCIENCE, 



EXPLANATION OF PLATE X, 



Illustrating Professor Van Beneden^s Researches on the 

 Dicyemidse. 



Fig. 1. — A young Bicyemopsis macrocephalus (prep, osmic acid im- 

 mersion, obj. 10, oc. 2). The head has not yet assumed the characteristic 

 form of the genus. It is still convex in front and the cells of the polar 

 velum are still arranged as they are in Bicyema typus. They are dis- 

 tinguished from the cells of the trunk by their finely granular appear- 

 ance. The parapolar cells still resemble the other cells of the trunk. 

 The whole ectoderm is very transparent, and a few granulations can just 

 be seen in the cellular protoplasm. The nuclei of all the cells are oval 

 and possess a nucleolus. In the cell of the endoderm there is seen — the 

 nucleus of the cell («), which is remarkable for its size, its elliptical form, 

 and exceedingly well-defined outline ; 2iidly, spherical spores or germs in 

 various stages of development, each having a small nucleus ; 3rdly, a 

 germ with two small homogeneous nuclei ; 4thly, a germ divided into 

 four segments; 5thly, two vermiform embryos at different periods of 

 development, seen in optical section, which are remarkable because in each 

 there appears to be a small central cell {e c) in the centre of the cephalic 

 cells, immediately in front of the endodermic cell, which will, perhaps, 

 become fused with the axial cell after the disappearance of its nucleus, 

 to form the male cell. 



Fig. 2. — The head of a very large Bicyemopsis macrocephalus (rhom- 

 bogenous) seen in optical section, and drawn from an individual lying upon 

 its ventral face. The polar velum is shown as it appeared when the ob- 

 jective was focussed to show the optical section of the organism in its 

 parapolar region. (Prep, in osmic acid, obj. 10, oc. 2.) The eight cells 

 of the polar velum are seen by transparency. The parapolar cells have 

 their characteristic form, they are of great size, and possess large oval 

 nuclei. In the axial cell is seen an infusoriform embryo fully developed, 

 and also the protoplasmic network. The embryo always presents many 

 refracting bodies in Dicyemopsis. 



Fig. 3. — Bicyemella Wageneri of Medone moschaia (obj. 8, oc. 2). 

 This represents a large nematogenous individual, whose movements 

 resemble in many ways those of Gregurina gigantea. The absolute 

 position of the folds remain unaltered ; but from the movements of 

 the organism their position in relation to the body of the Dicyemella 

 constantly changes. The ectoderm is finely granular ; here and there it 

 encloses larger globules, which are collected together at two points to 

 form warts {w, to). The constituent cells of the ectoderm are not distin- 

 guishable. In the clear endodermic cell, which is perfectly transparent 

 and absolutely free from granulations, germs and vermiform embryos 

 are seen in great number. 



Fig. 4. — Part of the endodermic cell of a Dicyemella oi Eledone tnoschata, 

 showing two germ producers and the nucleus of a germ producer («') 

 which has become free in the protoplasmic network (obj. 8, oc. 2). 



Fig. 5. — Germ producer oi Bicyemopsis macrocephalus (obj. imm. 10, 

 oc. 4). It comes from a rhombogenous individual which contained 

 only this one germ producer placed near the nucleus of the axial cell 

 {ri). The germ producer shows three generations of germs, arranged in 



