ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 63 
single fact of development to support it ; and this theory happens to be 
all wrong from beginning to end.” 
According to Whitman’s previous studies,* both the eyes and the 
segmental sense-organs develope as local thickenings of the epidermis. 
The ordinary metameric scnsillae are serially homologous with the eyes, 
and are connected with them by gradual steps of structural elaboration. 
They are double organs, both in structure and function, having an axial 
cluster of tactile cells and large, clear visual cells around and beneath 
these. So is it also with the eye. A double innervation of the eye in 
Hirudo and Aulcistomum has been detected by Maier, but he has failed to 
notice its significance. This is plain when we take the eye of Clepsine 
as our starting-point. There the eye-nerve is composed of two parts — • 
(1) optic fibres terminating in the visual cells, and (2) tactile fibres 
ending in the hair-cells. In the Hirudo eye it is likely that the tactile 
cells have been turned into visual cells, but the double nerve persists. 
The eye of a leech can form no image of external objects, but it has a 
“ photesthetic ” sensibility, shared by the metameric sensillae when these 
have visual cells. The suggestiveness of a series beginning with pure 
tactile organs and ending with pure visual organs is again pointed out. 
/3. Nemathelminthes. 
Spermatogenesis in Ascaris megalocephala.} — Dr. A. Brauer finds 
in the spermatogonia of the univalens variety a simple splitting of the 
chromatin grains ; these arrange themselves in a long thread, which 
separates into two segments— the final chromosomes. The result is two 
split or bipartite chromosomes. In the spermatocytes of the same 
variety there is a double splitting of the chromatin grains, and these 
arrange themselves on a thread which is not divided. The result is a 
doubly split or tetrapartite chromosome. 
In the variety bivalens there is a simple splitting of the chromatin 
grains, and these form a thread which divides first into two, then into 
four. The result is four bipartite chromosomes. In the spermatocytes 
there is a double splitting of the chromatin grains, and these form a 
thread which divides into two segments. The result is two tetrapartite 
chromosomes. 
The author has a long discussion of his results, which harmonize 
with those which he obtained from his study of Branchipus. 
Schneider’s Pore and (Esophageal Glands in Nematodes.} — Prof. 
0. Hamann has lately found Schneider’s pore and its canal in a large 
number of Adriatic Ascaridse, Strongylidae, and in Lecanocephalus. In 
the last-named the pore lies a short distance below the lips on the dorsal 
and inner wall of the oesophagus, and forms a communication between 
the lumen of this tube and an organ which lies in the wall of the oeso- 
phagus. The pore leads into a capillary membranous canal, which is 
surrounded by a granular substance, and may be traced to the neigh- 
bourhood of the sucking apparatus, which separates the oesophagus from 
* Journ. Morphol., i. (1887) ; ii. (1889). 
t Arch. f. Mikr. Anat., xlii. (1893) pp. 153-213 (3 pis.). 
X Zool. Anzeig., xvi. (1893) pp. 432-4. 
