38 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
The first organ to appear is the stomodfeum, which haB the form of 
a tube, the walls of which are at first one cell thick ; the position of the 
gut, before its formation, is shown by a large cylindrical mass of yolk, 
the central portion of which has a curious honeycombed appearance. 
While in Euscorpius the chelicerae do not appear till after five other 
pairs, in Scorpio they are the first to be seen ; in their earliest stages 
they are represented by a pair of solid outgrowths on the ventral 
surface. During the later stages of embryonic life the embryo nourishes 
itself by the destruction of a cord of cells w T hick form a coiled appendix 
to the stomodieum ; this cord is held in position by the chelicerae, so 
that we see the reason for the early appearance of those organs. 
Lateral Eyes of Spiders.* — Mr. K. Kishinouye states that he failed 
in his first study f of the development of the eyes of Spiders, to notice a 
very important stage. All their lateral eyes arise from a common 
thickening of the hypodermis on each side at the posterior, external 
corner of the lateral vesicle. 
This thickening is slightly invaginated and consists of cells arranged 
in many, irregular rows. Later on, the invagination disappears, and 
the hypodermic thickening is now flat above the lateral vesicle, which is 
at this time separated from the general ectoderm. 
A little later differentiation occurs at three places in the hypodermic 
thickening ; nuclei become a little larger and stain slightly less than 
those found elsewhere. These three groups form the retinal portion of 
the three lateral eyes ; they receive their nerves from a portion of the 
brain formed by the lateral vesicle. The latter, therefore, is the optic 
ganglion, formed from an invagination independently of the semicircular 
cephalic groove which gives rise to the brain proper. The common 
hypodermic thickening of the lateral eyes of Spiders is most probably 
homologous to the hypodermic thickening of the lateral compound eye 
of Livndus, as the position is the same in both, and in both an invagina- 
tion is similarly produced. The author is inclined to believe that the 
lateral eyes of Spiders are separated, enlarged and modified ommatidia 
of a compound eye of their ancestor. The history of development in 
the Scorpion would appear to be the same to judge from the account 
given by Parker ; while Lankester and Bourne arrived at this same 
conclusion, but stood in need of the embryological proof. 
Another point which the author claims as in his favour is that the 
number and the relative position of the simple eyes of Spiders and 
Scorpions vary very much. This separation and modification of the 
ommatidia of a compound eye into simple eyes are probably the effects 
of a change in the animal’s habits — it ceases to wander about in pursuit 
of prey and lies in wait for it instead ! 
€. Crustacea. 
Sensory Hairs of Crustacea.* — Prof. C. Claus calls attention to 
various passages in his numerous papers which describe the sensory 
hairs of Crustacea. The entrance and termination of the nerve in the 
hair, the difference between the axial part which consists of processes 
* Zool. Anzeig., xiv. (1891) pp. 381-3. f See this Journal, 1891, p. 163. 
J Zool. Anzeig., xiv. (1891) pp. 363-8. 
