ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
23 
In Proneomenia, as in Chsetoderma, the ova pass through the peri- 
cardium, whence a canal passes backwards on either side, and opens into 
the anterior end of the albumen-gland. Neomenia is clearly the most 
highly developed of these three genera in the structure of its generative 
apx^aratus. 
The various organs of the three forms are briefly compared with one 
anotber. The skin of Chsetoderma is very simple, that of Proneomenia 
gives rise to a thick chitinous cuticle, in which there are spicules, and 
Neomenia has a thick cutis, which is traversed by muscular fibres, 
nerves, and blood-vessels. The gonad of Chsetoderma is simple, and 
the sexes separate ; in the others, which are hermaphrodite, the gonad 
is double. In all three the circulatory organs are arranged in the same 
way, but the diaphragm is best developed in Chsetoderma ; the blood 
is led, and the corpuscles oval or rounded cells, with a central nucleus. 
The author has nothing new to add to the earlier descriptions of the 
nervous system. The musculature is best developed in Chsetoderma^ 
which has four strong longitudinal muscles ; in that genus also the 
digestive canal is more highly organized than in the other two. 
While Chsetoderma is by its musculature and skin (saving the 
calcareous spicules) most like an annelid, in other points of its organi- 
zation it is more closely allied to the Mollusca. Its large tooth, which 
must be regarded as a modified radula, its gills and gonads are those of 
a Mollusc. Proneomenia is more distinctly a Mollusc ; it has a well- 
developed radula, is hermaphrodite, and in some species (at any rate) 
has a penis. In Neomenia the molluscan character of the gonads is 
still more marked, for there is a receptaculum seminis on the efferent 
duct of the gonad, while the duct appears to be divided. The circulatory 
system is molluscan, for the blood filters through the tissues ; there are 
distinct blood-vessels in the skin of Neomenia only, but these do not 
seem to have a proper wall. 
S. Lamellibrancliiata. 
Variability of Tasmanian Unio."^ — Mr. E. M. Johnston has made 
a close study of a number of specimens of the genus Unio. He finds 
that, if specimens marking seven successive stages of growth be com- 
pared together, the variations in form from youth to the adult stage 
embrace characteristics which cover most of the distinctions upon which 
many of the Australian forms mainly depend for the recognition of 
distinct specific rank. He thinks it probable that the several forms 
erected into distinct species in various parts of Australia may ultimately 
l>rove to be local varieties or particular stages of growth of one widely 
distributed species. 
Molluscoida. 
a. Tunicata. 
Development of Pyrosom.a.t — Hr. 0. Seeliger confirms Chun’s 
oi)inion that the young colonies of four Pyrosowm-individuals usually 
pass from the cloaca of the mother animal to considerable depths, 
* Proc. Boy. Soc. Tasmania, 1888 (1889) pp. 95-6 (2 pis.), 
t Jenaisehe Zeitschr. f. Naturwiss., xxiii. (1889) pp. 595-658 (8 pis.). 
