ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
OQO 
OOO 
Thus Chodat, in his ‘Etudes de Biologie lacustre’ (1898), says that a. 
true lake must not be less than 20-30 metres in average depth, while a. 
true pond must not exceed about 15 metres. Intermediate basins may 
be called “ lake-ponds,” “ Seenteiche,” “ lacs-etangs.” But are there not 
biological criteria ? 
In lakes the plankton is much less diverse, and the dominant floating 
Algae are different. In ponds, Protococcaceoe, Palmellaceae, certain Des- 
mids ( Closterium cornu , Cl. pseudospirotsenium, &c.), certain Schizophyceae 
(. Anabsena , Aphanizomenon, and Polycystis') are much more abundant 
than in lakes. Another feature of ponds is the relative sparseness of 
diatoms in the micro-flora. Characteristic of ponds are such forms as 
Scenedesmus , Pedia* * * § trum, and li haphidium poly morph um . 
Species of the rotifer Brachionus, abundant in the “ Helioplankton 
of ponds, are relatively rare in lakes ; and Scliizocerca diversicornis and 
Pedalion mirum are also distinctively shallow-water forms. The author 
gives many other examples. 
Plankton of Swiss Lakes.* — Herr G. Burckhardt has investigated 
a large number of lakes, and gives lists of the Botifera, Cladocera, and 
Copepoda, with appended systematic and distributional notes. 
Period of Sexual Maturity in Marine Animals. f — Dr. S. Lo Bianco 
has published a list of a large number of animals from Porifera to- 
Pisces, in which he states the period of sexual maturity as observed in 
the Gulf of Naples. The list represents a big piece of work, and will 
be of much use for reference. 
Relation of Fauna to Bottom-Deposits.* — Mr. E. J. Allen has 
studied the relation of the fauna to the bottom-deposits along the thirty- 
fathom line from the Eddystone to Start Point. The causes which 
influence the distribution of life on the sea-bottom are discussed under 
two heads: — (1) Physical , the constitution of the sea-water, the nature 
of the bottom-deposit, the movements of the water, the temperature, 
the pressure, and the light; and (2) Biological, the advantageous and 
disadvantageous influences of animals upon one another. The bottom- 
deposits are grouped in eight grades: — stones, coarse gravel, medium 
gravel, fine gravel, coarse sand, medium sand, fine sand, and silt. 
Mr. Allen gives a vast array of tables showing the distribution of 
animals on the different grounds, and communicates a large number of 
faunistic notes. 
Teeth of Fish.§ — Mr. .T. H. Mummery has examined the teeth of 
Echeneis squalipeta, and finds them to display several peculiarities. 
The lower jaw projects so far in front of the upper that the teeth of 
the latter, when the mouth is closed, lie within those of the former. 
These projecting teeth have spatula-shaped crowns and are strongly 
recurved ; it is suggested that they may be used to scrape off parasites 
from the shin of the sharks to which the sucking-fish attaches itself. 
All the other teeth have simple conical crowns with recurved tips. 
The teeth are attached to the bones by a modified ball-and-socket 
* Zool. Anzeig., xxii. (1899) pp. 185-9. 
t MT. zool. Stat. Neapel, xiii. (1899) pp. 448-573. 
X Journ. Mar. Biol. Ass., v. (1899) pp. 365-542 (16 charts). 
§ Trans. Odontolog. Soc., xxxi. (1899) pp. 62-77 (2 pis.). 
