316 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
often a number. The renal gland-cells of the Monotocardia, on the 
other baud, do not produce a diffused concretion. The excreted liquids 
become concentrated into one place so as to form a spherical vacuole, 
which is placed near the periphery of the cell. This vacuole increases 
in size, and the salts contained in suspension in the liquid which forms 
it condense into a large concretion or, sometimes, into several smaller 
masses. The cells are not, as a rule, ciliated, but the presence or 
absence of cilia is a secondary matter. 
The mechanism of the urinary secretion varies as the secretion is 
diffuse or vacuolar; in the former case it seems to be merely effected 
by osmosis, but in the latter the vacuole escapes from the cell and falls 
into the renal cavity surrounded by a delicate protoplasmic envelope. 
The cell is reformed after the expulsion of the vacuole, and continues to 
exercise its function. 
M. Perrier applies the results he has obtained to a classification of 
the Prosobranch Gastropods, and, in an appendix, he institutes a com- 
jmrison between the renal organ of these and that of other Molluscs. 
Ife is led by it to agree with de Meuron in comparing the larva of a 
Mollusc with that of an Annelid, with this difference, that in place of a 
chain of a number of somites there are in the Mollusca only two. 
Blood and Lymph-gland of Aplysiae.* * * § — M. L. Cuenot finds that 
the blood in the heart of the Atlantic Aplysia clepilans is distinctly rosy. 
This coloration is due to the presence of an albuminoid, and has no 
relation to the absorption of oxygen. The albuminoid, which is distinct 
from htemocyanin, may be called hgemorhodin. The blood of the 
Mediterranean A. punctata is quite different, for it contains colourless 
hmmocyanin. The amoeboeytes ajipear to be formed by the crista aort£B. 
This is a large hollow dilatation of the anterior aorta which has some- 
thing of a glandular appearance ; it is inclosed with the heart in the 
pericardium. When an injection is forced in, it swells up like an 
orectile organ, but returns to its normal dimensions when the pressure 
ceases. Its wall is formed by a thick felting of connective tissue and of 
elastic fibres which anastomose and divide in all directions. Among 
these are masses of nuclei, a large number of which are surrounded by 
protoplasm ; these are evidently mature amcebocytes which are ready to 
pass into the blood. Somewhat similar structures have been observed 
in Philine and Scaphander. 
Pleurophyllidiidse.j — Dr. E. Bergh gives a systematic review of 
this group ; in the forms newly examined by him he observed that the 
buccal armature varies in the different species in a way never noticed in 
any other group of Nudibranchs. 
Structure and Functions of Cerata in some Nudibranchiate 
Molluscs.}: — Prof. Herdman here enters into some greater details as to 
the structure and functions of the cerata of Molluscs, than in the report 
we noticed some months since. § Full illustrations are now given. 
* Coraptes Kendus, cx. (1890) pp. 724-5. 
t Abh. Zool.-Bot. Gesell. Wien, 1889, pp. 1-14 (2 pis.). 
X Quart. Journ. Micr. Sci., xxxi. (1890) pp. 41-63 (5 pis.). See also Rep. Brit. 
Assoc., 1889 (1890) pp. 630-3. 
§ See this Journal, 1889, p. 627. 
