902 . DR. E. L. MOSS ON THE ANATOMY OF 
tens observed, is sometimes formed, but is invariably more transparent and delicate than 
its predecessor. When the Appendicularia has remained long in the structure, its upper 
part generally contains a few oval excrementitious masses, adhering to its viscid mem- 
brane; and as such masses are less frequently met with in the * Haus ” formed under 
observation than in that found floating tenantless in the ocean, it is probable that the 
animal in its natural state makes a more lengthened residence in it than might otherwise 
be supposed. When microscopically examined, the * Haus" is found to be a sae of 
extreme tenuity, with a deep longitudinal groove ending above, where the animal was 
attached, in a torn fissure, and pierced below in the middle line by two small openings 
with projecting funnel-shaped lips. On either side the sac opens into a short tube of 
considerable diameter, marked with parallel longitudinal ridges. The membranes of the 
sides of the above-mentioned fissure are the most readily seen parts of the structure; in 
them two sets of parallel bars cross each other at right angles, and thus form a reticulation 
of great beauty and regularity—so regular, indeed, as closely to resemble the markings on 
a micrometer (fig. 7, c). In a large * Haus" in which this structure was first observed, 
the areolations measured :0018 by -0037 of an inch. During the process of evolution 
the terminations of the more finely marked bars are attached to the lips of the branchial 
orifice. The netted membranes are folded upon themselves in such a way as to look like 
a pair of lateral sacs, except when seen from above, when they present the fan-like 
appearance shown in the * Haus" figured by Professor Allman in the *Journal of 
Microscopical Science for 1859.’ - 
Some interest may perhaps attach to the chemical constitution of the “Haus.” It gives 
no nitrogenous smell when burnt, and is insoluble in water, alcohol, ether, solution of 
potash, or the dilute mineral acids; in a word, it possesses the negative characters of 
Tunicin. 
The geographical range of the Appendicularie is at least as extended as that of any of 
their pelagic brethren. Their discoverers found the first specimens in Behring’s Straits 
and in the South Pacific; and those which gave materials for this paper were captured 
in the Mediterranean and the Gulf of Mexico, as wellas over a large Atlantic area extend- 
ing from the southern Tropics to the cold green waters of the Labrador current. 
