954 THE AMERICAN NATURALIST. [Vow. XXXII. 
The spring plankton is characterized by the predominance of dia- 
toms and a great increase in the amount of ash, which precludes any 
direct comparison with land plants. If, however, the comparison be 
based upon the ash-free substance of the diatoms, it is found that 
this differs from the richer food plants only in the greater proportion 
of fat, as the following table shows. 
Per Cent Dry WEIGHT. ALBUMEN. Fat. icra gol 
Lupine — extra quality .... . 29.3 2.8 67.8 
Prous (kerno) 6062 eo ee 2752 2:3 70.4 
Dratomss ow ee y 28.7 8.0 63.2 
The summer plankton is predominantly animal, and thus presents 
a large amount of albumen, a fat-content at times low, at times 
abnormally high, and a relatively very small amount of carbo- 
hydrates. In these particulars its analysis resembles those of fish, 
mussels, and other marine animals. raat A 
ZOOLOGY. 
Morphology of Trematodes. — An interesting contribution to 
trematode morphology is contained in the recent paper by Pratt in 
the Zoologische Jahrbücher? An investigation of Apoblema appendicu- 
datum has brought to light a condition of the body covering which 
throws light upon the unsettled question concerning the nature of the 
outer layer of the body, or “ cuticula,” in trematodes and cestodes. 
Five principal views have been advanced concerning the nature of 
this layer. The older view of Schneider ('73) and Minot ('77) was 
that the layer is a basement membrane from which the overlying 
epithelium has been lost. Ziegler (83) made the suggestion that the 
cuticula is to be regarded as an epithelium in which the nuclei, cell 
boundaries, etc., have become obliterated, a view which has attained 
considerable acceptance from the support given it in recent years by 
the writings of Braun and Monticelli. Brandes ('92) advanced the 
view that the layer arises as a secretion of the submuscular cells 
Pat H S A Contribution to the Life-History and Anatomy of the 
Appendiculate Distomes, Zoologische Jahrbücher, Abth. f. Anat., Bd. xi (1898). 
