ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
29 
renal organs of Solenomya and Fissurella are much more similar to ono 
another than are those of the former and most Lamellibranchs, or of the 
latter and most Gastropods. The resemblance between the excretory 
organ of the Protobranchiata and that of the more primitive Rhipido- 
glossata is made still more complete by the fact that in the former 
(. Nucula , Leda, Yoldia . Solenomija) the gonads open into the kidneys as in 
the Fissurellidse, Haliotidse, &c. ; an arrangement known in only three 
of the higher Lamellibranchs. 
Molluscoida. 
a. Tunicata. 
Origin of Test-cells of Ascidians.* — Dr. T. H. Morgan, who has 
examined various forms, describes especially the history of the test-cells in 
Cynthia ocellata and Clavellina sp. In the former the test-cells arise from 
follicular cells of the egg, which take up a more internal position ; at 
the stage when the follicular cells are thus migrating two main sources 
of error may arise : — if the section passes near one end of the egg, when 
the convexity of the surface is so great relatively to the plane of the section 
that two or more layers of the nuclei of the follicle may appear in 
the same section; or an error may arise if the microtome knife does 
not cut the egg cleanly, but turns over part of the follicular zone. The 
author refers so constantly to his figures that we cannot trace with him 
the various stages in development. In later stages the test-cells do not 
seem materially to change either in number, size, or structure, but the 
follicular cells continue to increase in size and become much vacuolated. 
In young ova the follicular cells were found from surface views to have 
irregular outlines, and in general appearance to resemble peritoneal 
epithelial cells. Dr. Morgan’s results agree essentially with those of 
Yan Beneden and Julin, and are diametrically opposed to those of 
David off. 
£. Bryozoa. 
Cyclatella annelidicola.f — M. H. Prouho gives an account of this 
organism. It was first seen by MM. Yan Beneden and Hesse on the 
integument of a Clymene , and was by them regarded as a Tristomid, 
though its resemblance to a Loxosoma was noticed. Leuckart believed 
it to be a Bryozoon, and with him Nitsche agreed, while Schmidt upheld 
its Trematod character, though Yan Beneden was converted by the 
arguments of Leuckart. 
M. Prouho cannot doubt that it is a Loxosoma , although specifically 
different from any species yet described as belonging to that genus. It 
has the two lobes of the calyx greatly developed, and the other characters, 
none of more than specific value, are enumerated and discussed. 
Arthropoda. 
Relationships of Arthropods.^ — Prof. H. T. Fernald discusses the 
relationships of Arthropods. He commences with an account of the 
* Journal of Morphology, iv. (1890) pp. 195-204 (1 pi.). 
t Comptes Rendus, cxi. (1890) pp. 799-801. 
X Stud. Biol. Lab. Johns Hopkins Univ., iv. (1890) pp. 432-513 (3 pis.). 
