ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
467 
folds of ectoderm in the sensory notch, while in the Pelagia- stage of the 
Chrysaora the rudiments of the folds have appeared, and in this species 
and Dadylometra quinquecaria the dorsal groove does not appear until 
the second set of tentacles begins to form. The Chrysaora-st&ge in the 
1 dadylometra has the paired folds more developed than in the beginning 
of the adult stage in the Chrysaora , and different from what they are in 
the fully-formed adult of that species. Of the adult sense-organs in the 
three species, those of Dadylometra are the most highly developed. It 
appears, then, that in Pelagia , Chrysaora , and Dadylometra , there is, 
with increased complexity of general characters, an increase, both 
phylogenetically and ontogenetically, in complexity of the sense-organs ; 
but the steps in the ontogeny of these organs are not strictly identical 
with the condition at the corresponding points in the phylogeny of the 
species. 
Portuguese Man-of-War.* — Mr. R. P. Bigelow has had the oppor- 
tunity of making some observations on the physiology of Caravella 
maxima Haeckel — the Portuguese Man-of-war. This Medusa feeds 
almost entirely on small fish, which are caught by running against its 
tentacles. The tentacle is immediately firmly attached to the fish, 
probably by the nettle-cells, and it is very soon temporarily paralysed by 
the poison from them. Before, however, the fish succumbs it manages 
to give a pretty vigorous pull on the tentacle. This acts as a stimulus 
to cause the tentacle to contract, the impulse apparently coming from 
the base. If the fish offers no resistance the tentacle does not contract. 
By the contraction of the tentacles the fish is brought into contact with 
the mouths of some of the siphons, the feeding members. These mouths 
are spread out over the fish until they completely envelope it. It is 
there finally killed and digested. The products of digestion with 
indigested fragments are taken into the stomachs of the siphons until 
they are gorged ; digestion is completed in the stomachs, and the 
nutrient fluid is conveyed by the hollow pedicels to the rest of the corm. 
A siphon will attach itself with equal alacrity to a piece of fish or to a 
small stone, but does not remain attached to the latter very long. 
The beating of wind or rain against the float causes its muscles to 
contract, so as to erect the crest, which normally lies flat on the water. 
It seems to require a good deal of effort to keep the crest erect. 
The secretions observed were a mucous secretion on the surface, a 
gluey substance at the mouth, a digestive fluid, a poison in the nettle- 
cells, and, probably, the gas in the float. 
The nervous system seems to be very poorly developed. There is 
some indication of a motor centre at the base of each tentacle, and 
impulses may be transmitted from one part to another. No correlation 
of movement was seen. There are no traces of any sense of sight, 
hearing, or smell ; and it is doubtful whether there are any special 
senses. 
Tetraplatia volitans.f — In the fourth of his memoirs on the lower 
animals of the Bay of Algiers, Dr. C. Yiguier treats of this rare and 
interesting Coelenterate. So far as is known it is pelagic, but it is 
* John Hopkins Univ. Circ., ix. (1890) pp. 61-2. 
t Arch, de Zool. Expe'r. et Gen., viii. (1890) pp. 101-42 (3 pis.). 
