1893.] ; Zoology. 389 
from the ectoderm by the mesoderm. Later it becomes elevated 
from the yolk, forming a small cavity open to the yolk, the future 
mesenteron. This layer is regarded by Korschelt as entoderm, and has 
been regarded by several authors as the proctodeal inpushing. He also 
finds the nervous system to be, as might have been expected, ectoder- 
mal. Dr. Burckhardt described the central nervous system of the 
Dipnoi. He has subjected the brain to sections, and by study of these 
has been able to elucidate points not before understood. He concludes 
that in its brain Protopterus is not an Amphibian, but that it is in this 
respect a problematic organism between the fishes (Elasmobranchs) 
and Amphibia, whose exact position will first be solved when the 
ontogeny is studied. Professor R. Hertwig had a review. of recent 
work upon canjugation and fertilization, and Dr. H. H. Field a paper 
on the Metamerism of the Kidney of Amphiuma, already noticed in 
our pages. The last paper was a’ view of the idea of instinct, by Pro- 
fessor H. E. Ziegler. | 
Eyes of Polychætes.—Dr. E. A. Andrews has an extended 
article? on this subject. He has studied a large series of genera, some 
both as young and adult, and among the conclusions at which he 
arrives are the following: The eye is an epidermal organ consisting of 
a pigmented cup containing a refracting mass, which at the orifice of 
the cup comes in contact with the cuticle. The wall of the cup con- 
sists of a single layer of cells forming the retina, each retinal element 
containing pigment, and being produced internally into a nerve pro- 
cess, externally into a clear rod. This, as will be seen, is a different 
conception of the annelid eye from either that of Carriére or that of 
Graber, but one which approaches most nearly to that of the former 
author. 
Arachnida.—Mr. B. I. Pocock discusses’ the external anatomy of 
the members of the group Arachnida (s. s.), and concludes that the 
members must be arranged in two sub-classes, Ctenophora, with the 
single order Scorpiones, and Lipoctena, containing the superorders 
Caulogastra (Pedipalpi and Aranez) Mycetophora (Solifuge), and 
Holostomata (Pseudoscorpiones, Opiliones, Acari). 
F. Purcell, after studying the anatomy and development of the eyes 
of Liobunum hemisphericum, concludes‘ that contrary to the com- 
2Jour. Morph., vii, 169, 1892. 
3Ann. and Mag. Nat. Hist., VI, xi, p- 1, 1893. 
4Zool. Anz., xv, 1892. 
