482 SIR J. LUBBOCK ON THE DEVELOPMENT 
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Possibly one principal function of the branchiæ is to produce constant currerits, 
thereby bringing fresh supplies of water into contact with the general surface of the skin, 
through which doubtless much of the respiration is carried on. 
On the other hand, there are species to which (as, for instance, is the case with Ephe- 
mera vulgata) this argument does not apply. : 
According to Rathke, “the muscles by which these movements are produced are ex- 
ceedingly simple. Each segment which takes part in it is furnished only with a single 
pair of muscles for this purpose, each of which is attached by one end to the lateral wall, 
and by the other to the dorsal wall or plate, in both places close to the soft parts of the 
cutis "'*, 
In the same manner Chabrier t tells us that the wing-muscles do not (except appa- 
rently among the Libellulidæ) act directly on the wings, “mais ils les meuvent par 
l'intermédiaire du dorsum et par d'autres leviers particuliers." Some light seems to be 
thrown on this remarkable fact by the above-mentioned statement of Rathke; and the 
movement of the branchiæ in aquatic larvæ forms a connecting link between the two, 
and throws some light on the curious arrangement of the muscles observed by Chabrier. 
The Digestive Organs. 
The esophagus is very short indeed, and expands immediately behind the head into 
the stomach, for which there is plenty of room even in the thoracic segments, owing to 
the weakness of the legs and the smallness of the muscles by which they are moved. 
The ilium is quite short and well rounded. The rectum is rather longer, and cylindrical. 
The Malpighian vessels are numerous and short. They open as usual into the posterior 
end of the stomach. According to Burmeister the Neuroptera have six Malpighian vessels ; 
in this species they are, however, more numerous and of a somewhat peculiar form, con- 
sisting of two parts, which are about equal in length. The distal portion consists of à 
thin cylindrical tube. The other half is shaped like a long club, to the broad end of 
which the cylindrical tube or efferent duct is attached. Swammerdam (Bib. Nat. 
plate xv. fig. 5), who is quoted by Ramdohr (Verdauungswerkzeuge der Insekten 
p. 151), does not figure or mention any Malpighian vessels. It is true that his observ 
tions did not refer to the same species as mine; but it seems unlikely that the different 
species of Ephemera should differ from one another in a point of so much importance. 
The Malpighian vessels are formed of nucleated cells in the usual manner. Under the 
action of acetic acid, they become quite transparent. 
The food consists principally of minute Diatomacex. Swammerdam, indeed, says that 
the larvæ of the Ephemerid feed on mud; but this js probably a mistake arising from 
the small size of the Diatoms and the low powers used by him. Still it is quite possible 
that it may be true of the species examined by him. Other species, again, according s 
Pictet, are insectivorous. 
* : : 
.* Loe. cit. p. 83. + Vol des Insectes, p. 33. 
