600 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
of a larger series of organs and parts of organs in Pandalus cinnulicornis 
(two races) and Palsemon serratus (one race), but not more than one 
hundred individuals of each race have as yet been examined, and the 
curves of distribution of the magnitudes of the various organs are there- 
fore more irregular than those given for the shrimp. 
Circulatory System of Carapace of Decapod Crustacea.* — M. E. L. 
Bouvier states that the afferent system of the membrane which lines 
the carapace in the branchial region arises from a large postcephalic 
lacuna which surrounds the liver and carapace; the efferent system 
consists of a well-defined trunk which follows the membrane close to the 
free border of the carapace ; it increases in size from before backwards 
and opens directly into the pericardium at its posterior angle (Astacus) 
or at the sides. There is, in fact, a cutaneous respiratory apparatus 
analogous to that of My sis, and it is the exaggeration of this arrange- 
ment which allows certain Crustacea, such as Birgus latro , to live for a 
very long time out of water. 
In other words, the Schizopods and the abranchiate larvae of Decapod 
Crustacea, have a purely cutaneous mode of respiration ; in the adult 
Decapod this respiratory apparatus persists, and in some of its characters 
is constant ; but to it there has been superadded a secondary respiratory 
apparatus, the branchial, and this is the only one which is, as a rule, 
described in our text-books. 
Histology and Development of Eye of Lobster, f — Mr G. H. 
Parker gives an account of the minute structure and development of the 
eye of the Lobster. The ommateum, which lies between the corneal 
cuticula and the basement membrane, is composed of cells of the corneal 
hvpodermis, cone-cells, distal retinuhe, proximal retinulae and accessory 
pigment-cells, each of which the author describes in order. The view 
that the corneal cuticula is separated from the cone-cells by an inter- 
vening layer of cells is one which has been held only by recent investi- 
gators ; though Claus suspected the presence of a corneal hypodermis he 
searched for it in vaiu. Each hypodermal square appears to consist 
of two flattened cells, triangular in outline and very intimately applied 
to one another on their longest sides. The author supports the view of 
Schultze and Grenacher that the cone-cells and rhabdoms are separate 
structures, and it is probable that in the crayfish, as in the lobster, the 
fibrous ends of the cone-cells terminate in the basement membrane. 
The distal retinulae have not as yet been identified in the eyes of many 
Decapods, though Carriere has seen them in Astacus. In the region of 
the retina which lies between the proximal ends of the cones and the 
distal border of the deeper band of pigment, the groups of cone-cells 
and the pairs of distal retinulae are separated by a considerable inter- 
vening space ; the space is filled by a fluid which contains a very small 
amount of albuminoid substance; on coagulation it forms vesicular 
bodies of varying size, which usually become loosely attached to the 
cone-cells and the fibres of the distal retinulae ; they readily take up 
colouring matter, and it was probably these bodies which Newton 
described as the nuclei on the investing membrane. 
* Comptes Rendu3, cx. (1890) pp. 1211- 3. 
| Bull. Mus. Comp. Zool., xx. (1890) pp. 1-GO (2 pis.). 
