442 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Circulatory System of Dreissensia polymorpha.* * * § — M. Toureng 
notes that this form, divergent from the Mytilidee as regards its nervous 
system, is remarkable in its circulatory arrangements. Thus, there is 
a large posterior aorta, and the rectum occupies its cavity. A cross 
section shows the doubly contoured blood-vessel surrounding the gut, 
and its structure suggests that it arises from the confluence of two 
vessels. At the anterior third of the adductor, the posterior aorta gives 
oft’ two pallial arteries, each of which divides into a dorsal and a ventral 
branch. The ventral branches unite with the anterior pallial arteries 
to form the circumpallial vessels. Pericardial, rectal, gastro-intestinal, 
viscero-pedal, and hepatic arteries are also described. 
Molluscoida. 
a. Tunicata. 
So-called Segmentation of the Tail in Appendicularia-t — Dr. 0. 
Seeliger finds in Fritillaria furcata and Oikopleura cophocerca that each 
of the seven so-called “ muscle-segments ” is a large muscle-cell. The 
contractile substance forms parallel lamellae of fibrils on the side of the 
cells towards the chorda, and extending continuously along the whole 
length of the tail. Moreover, it is to be noted that the ganglia do not 
correspond in number nor in distribution with the segments, and are 
variable. 
Degeneration of Distaplia.J — M. Caullery has studied a degenera- 
tive process affecting colonies of Distaplia rosea D. V., and confirms 
some results recently published by Salensky. But he does not seem 
to believe in Salensky ’s “ symphagocytes,” nor in the return of liberated 
cells to the tunic and nutritive stolons, there to be transformed into 
mesenchyme. The dominant phenomenon of the whole degenerative 
process is phagocytosis. 
Caullery also notes that the testa-cells arise by mitosis from follicular 
cells and not by a budding of the germinal vesicle ; that the cells of 
the testa do not contribute to the formation of the tunic ; that the peri- 
branchial cavity of the oozoite is formed entirely from two ectodermic 
invaginations ; that the tail of D. rosea degenerates as Kowalewsky 
described in Phallusia ; that the colonies of D. magnilarva are unisexual, 
for one of the sexual organs of the hermaphrodite bud degenerates 
finally at an early date. 
j3. Bryozoa. 
Bryozoa of Hungary. § — Dr. E. Vangel finds that about two-thirds 
of the European Bryozoa occur in Hungary, though only two species 
have been hitherto recorded. His preliminary list takes notice of ten 
species. 
Arthropoda. 
Derivation and Homologies of some Articulates. || — Prof. J. D. Dana 
prefers the term Articulates to Arthropods, as he considers that Crustacea 
* Comptes Rendus, cxviii. (1894) pp. 929-30. 
f Zool. Anzeig., xvii. (1894) pp. 162-5. 
j Comptes Rendus, cxviii. (1894) pp. 598-600. 
§ Zool. Anzeig., xvii. (1894) pp. 153-5. 
|| Amer. Journ. Sci., xlvii. (1894) pp. 325-9; reprinted in Ann. and Mag. Nat. 
Hist., xiii. (1894) pp. 502-6. 
