336 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
In Triarthrus the thoracic legs near the head are composed of compara- 
tively long joints, and the endopodite is seen to be adapted for crawling, 
and the exopodite for swimming. In the pygidial region the proximal 
part of the endopodite forms a paddle-like organ. In a young form a 
striking resemblance may be seen to the endopodites of Apus or to 
a typical phyllopod limb. 
Artificial Segmentation of Lininlus.* — Mr. W. Patten finds that 
gravity seems to determine the position of the blastopore, but has no 
influence on the position of the embryo, or on its planes of symmetry in 
reference to the blastopore. He notes that apparently insignificant 
changes in external conditions are capable of producing profound modi- 
fications of the normal mode of growth. One result of his observations 
is to confirm him in his belief in the relationship of Limulus to Verte- 
brates. If, that is, the eggs of IAmulus under abnormal conditions 
segment mesoblastically and develope “ yolk blastopores ” like those of 
Ganoids and Amphibia, it is regarded as almost certain that if these 
conditions became constant their result would become constant too. 
€. Crustacea. 
Luminous Organs and Compound Eyes.f — Prof. C. Chun makes an 
interesting contribution towards an understanding of the conditions of 
vision at great oceanic depths. His investigations relate to the Euphausise, 
which are of especial interest, since they occur both at the surface, and 
in abyssal darkness. It is therefore possible to study their adaptations 
comparatively. 
The luminous organs. — Besides the stalked eyes, there are similar 
organs on the sides of the thorax, and between the four anterior abdomi- 
nal legs. Claus called them (1863) “accessory eyes,” Murray and Sars 
proved their intense “ phosphorescence.” Sars also isolated the striated 
body in the centre of the organs, and showed that it was the seat of the 
luminosity. 
In young forms there is, as Sars showed, a small luminous organ 
beneath the eye, except in the blind Bentheuphausia. 
It lies on the posterior external surface of the facetted eye, and is 
simpler than those on thorax and abdomen. It consists (1) of a para- 
bolic reflector or tapetum, perforated by the nerve and covered by 
transient cinnabar-red pigment ; (2) of concentrically disposed lateral 
lamellae ; (3) of the central “ fibrous fascicle,” or “ striated body,” or 
“ luminous body/’ ; and (4) of a layer of cells between the luminous body 
and the reflector. The essential luminous body is formed of a radially 
arranged series of lamellae enclosing a central space with elongated 
cylindrical cells. Sars spoke of this organ as fixed, but, in Euphausia 
gracilis , Chun has seen it move, and has demonstrated the associated 
striped muscle fibres. 
The thoracic and abdominal organs are usually smaller, but they are 
more complicated. Thus they have a dioptric lens arrangement. They 
are moved by muscles, and throw their light in various directions. If 
compared with an eye, the lens would represent a crystalline cone, the 
* Zool. Anzeig , xvii. (1894) pp. 72-8. 
t Biol. Centralbl., xiii. (1893) pp. 544-71 (8 figs.). 
