510 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
in abundant multicellular sense-organs in tbe integument. These are 
sometimes definitely arranged, and are composed of bipolar nerve-cells. 
Nervous System of Nereis.*— Mr. J. J. Hamaker has made a de- 
tailed study of the central nervous system in Nereis virens Sars. The 
system lies deeper than in most Polychseta, is separated from the hypo- 
dermis by the circular muscles, and is protected by a spongy (ectodermic) 
neuroglia and an outer (mesodermic) neurilemma. 
The “ mushroom bodies ” of insects and Decapod Crustacea are re- 
presented in the brain of Nereis by the anterior masses of small nuclei. 
The optic ganglion, which in some species of Nereis lies beneath the 
anterior eye, may in other species lie within the brain-capsule. There 
is no neuropil in the ventral nerve-cord. Three longitudinal connec- 
tives run between each two successive ganglia, one small median and two 
larger laterals. The sheaths of the nerve-fibres have no nuclei, and must 
therefore be a product of the fibres. The cells have commonly one or 
more centrosomes. The giant fibres are nervous, and are put into rela- 
tion with peripheral organs through ordinary centrifugal fibres. The 
giant fibres give off no fibrillations, and nervous relation with other fibres 
is established directly between the axis cylinders. Certain decussating 
fibres are always united in pairs by anastomoses between the axis cylin- 
ders where they cross each other. Certain centripetal fibres of the same 
set are always united by anastomoses between the ends of the branches. 
Contact between axis-cylinders may possibly be one of the means of 
bringing nerve-fibres into functional relation with each other. 
Heart-body and Coelomic Fluid in Polychaeta .f — Mr. L. J. Picton 
has investigated Audoinia filigera , Pectinaria belgica, Siphonostoma diplo - 
chsetos, Polymnia nebulosa , Amphitrite variabilis, ^c. The mesoblastic 
origin of the heart-body is shown in Polymnia ; it is not homologous 
with the diverticulum of the gut which projects into the dorsal vessel in 
some Oligochaeta. The organ may be regarded, as Eisig suggests, as of 
the nature of intra-vascular chloragogen, that is, as modified peritoneal 
tissue, primitively clothing the outside of the dorsal vessel, but becoming 
folded so as to lie within it. It may be in part compared to the liver 
of Vertebrates, but there is no glycogen. Fat and iron are present, 
and the latter is probably associated with haematopoietic function. With 
regard to the mechanical functions of the heart-body, we are on surer 
ground. The vessel wall contracting upon it obliterates the heart 
cavity at systole, the whole of the blood passing to the gills. 
Owenia.J — Prof. G. Gilson has continued his study of Owenia fusi- 
formis, and has reached the following results. There is no peritoneal 
membrane on the parietal surface of the coelomic cavity. The body- 
wall is formed of musculo-glandular elements, and not by separate 
layers of muscular and glandular cells. The internal portion of these 
musculo-glandular elements secretes albuminoid substances, fatty matter, 
and uric products. The albuminoid substances form the spermatic 
plasm in the male and an envelope for the eggs in the female. As 
the nephridia have lost excretory function, this is discharged by the 
* Bull. Mus. Comp. Zool. Harvard, xxxii. (1898) pp. 89-124 (5 pis.). 
t Quart. Journ. Micr. Sci., xli. (1898) pp. 263-302 (4 pis.). 
% La Cellule, xiv. (1898) pp. 89-107 (1 pi.). 
