ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
69 
arise eacli from a single mesoderm-cell, while the vesicle and its canal 
are formed from two ectodermic cells. The paper includes a detailed 
criticism of Ziegler’s results. 
Central Nervous System of Anodonta.* — Herr T. Freidenfelt has 
a preliminary note on his researches on the above subject. The paper 
is chiefly concerned with histological detail, and the main point of 
general interest is the statement that the osphradium of Anodonta has 
no definite function, and that, in Acephala in general, the osphradia are 
rudimentary organs. 
Artbropoda. 
Relation of Arthropod Head to Annelid Prostomium. j — Mr. E. S. 
Goodrich discusses this morphological problem. The prostomium 
(Huxley, = Kopflappen, lobe cephalique') is a median anterior process, 
lying above and in front of the mouth, and varying greatly in size and 
form. It is attached to the peristomial segment, which is usually 
modified in connection with the mouth. It may be (1) a modified 
or reduced segment; (2) an incipient segment; (3) not a segment at 
all, but a structure of different and special nature. It is the last inter- 
pretation which the author seeks to prove. 
A typical segment is a region more or less distinctly marked off 
from the rest of the body by transverse grooves, surrounding the ali- 
mentary canal, containing a special coelomic cavity (more or less com- 
pletely separated off from the coelom of adjoining segments by means of 
transverse septa), a pair of nephridia and of peritoneal funnels com- 
municating with the exterior, a pair of ganglionic enlargements of the 
ventral longitudinal nerve-cords, and (in Polychsetes and Arthropods) a 
pair of appendages. But such fully equipped segments are rarely found 
in nature ; the embryological test is the decisive one. The peristomium 
fulfils the test ; but the prostomium presents none of the characters es- 
sential to a segment. Goodrich’s views in regard to the homologies of 
the head-region in Arthropods are summed up — not dogmatically, of 
course — in the following table. 
Annelida. 
| Peripatoidea. 
Insecta. 
| 
Arachnida. 
Crustacea. 
Prostomium with or with- 
Frontal processes ? 
? 
? 
? 
out tentacles, archicerebrum. 
Frontal processes. 
Segment 1. Peristomium 
Procephalic lobes, 
' Procephalic lobes, 
■ Procephalic lobes, 
Procephalic lobes, 
antennae, proto- 
protocerebrum. 
protocerebrum. 
protocerebrum. 
cerebrum. 
2 . 
Mandibles, 
Antenna-, deuto- 
Chelicerae, deuto- 
First antennae, 
deutocerebrum. 
cerebrum. 
cerebrum. 
deutocerebrum. 
„ 3. 
Oral papillae. 
Rudimentary- 
Trunk segment. 
Second antenna*, 
appendage, trito- 
tritocerebrum. 
cerebrum. 
,, 4. 
Trunk segment. 
Mandibles. j 
„ 
Mandibles. 
„ 5. 
Do. 
First maxillaj. i 
First maxillae. 
„ 6. 
Do. 
Second maxillae. | 
" 
Second maxillae. 
* Biol. Centralbl., xvii. (1897) pp. 808-15 (2 figs.), 
t Quait. Journ. Micr. Sci., xl. (1897) pp. 247-68 (12 figs.). 
