ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
619 
degeneration of the sole, the approximation of the genital pores, a 
change to carnivorous diet, with the consequent shortening of the gut, 
and other characteristic features. 
S. Lamellibranchiata. 
Gills of Lamellibranchs.* — Dr. F. Janssens appears to find himself 
in greater agreement as to the morphology of the gills of Lamellibranchs 
with the late Mr. Peck than with any other of the numerous observers 
of these organs. 
The author commences his account of his own observations by 
describing the general anatomy of the gill in various forms. In con- 
sidering the histological constitution of the gill he deals separately 
with the parts formed from the mesoblast and from the hypoblast, but 
his method of description, in which he constantly refers to figures, and 
the complete absence of any general deductions, make the paper one 
which can only be properly studied with the illustrations at hand. 
Molluscoida. 
a. Tunicata. 
Perivisceral Cavity of Ciona. f — Mr. A. H. L. Newstead finds that the 
primary condition of the epicardium is undoubtedly that found in Clavel- 
lina , where it has the function of a budding organ. In Ciona there is 
considerable modification and loss of the original function. The view 
of Herdman that the stolons of Ciona are modified budding organs 
appears to be correct. 
The view of Koule that the perivisceral cavity of Ciona is a primitive 
condition is not supported by Mr. Newstead’s observations, which point 
rather to the cavity being a specially modified epicardium which has 
become greatly enlarged. The space in question is certainly not 
homologous with the general blastocoel space of Appendicularia ; and there 
are no reasons for supposing that the other simple Ascidians pass 
through a stage in which the epicardium is enlarged as in Ciona ; in 
fact, so far as the perivisceral cavity is concerned, Ciona is the most 
modified of the simple Ascidians. 
Development of Tunicates.J — Herr J. Hjort finds that the only kind 
of budding in Botryllidse is that described by Metschnikoff and Della 
Yalle as pallial, and that the stolons are purely ectodermic in origin. 
He describes the early stage of the bud in which there is a median 
vesicle, from the dorsal part of which the blind dorsal tube grows 
forwards, while the two peribranchial vesicles appear laterally. In the 
posterior third of the bud these structures are all connected, and from 
this region the coiled gut grows backwards. The dorsal tube differen- 
tiates into hypophysis and permanent ganglion. In regard to the heart, 
Hjort observes that it arises from an unpaired compact mass of cells on 
the right side. As to the gonads, the results of Della Yalle are 
confirmed. 
From a study of the larva of Distaplia magnilarva , the author comes 
* La Cellule, ix. (1893) pp. 71-91 (4 pis.). 
t Quart. Journ. Micr. Sci., xxxv. (1893) pp. 119-28 (1 pi.). 
J MT. Z. Stat. Neapel, x. (1893) pp. 584-617 (3 pis.). 
