10 
these parts: they consist merely of a cellular capsule with spicules 
and interspieular substance in the interior, and their wall is the 
direct continuation of the cellular layer subjacent to the mus- 
eular coat. This coat is of course pierceed by the neck of the 
ingrowth, which. were it not filled up with spicules and inter- 
spicular substance, would certainly be looked upon as some secret- 
ing apparatus. 
Finally I must mention two symmetrically placed structures, 
which, judging by their size, have some important function in the 
economy of the animal and appear to belong naturally to this 
group of tegumentary formations. 
The organs alluded to are situated in the posterior extremity of 
the body and may briefly be characterized as a pair of coeca partly 
filled with a special secretion of an apparently cuticular nature, 
which is elaborately chambered more or less in the shape of a 
honey-comb. The coeca are in open communication with the anal 
cavity. Their walls are formed by a cellular layer (fig. 32, Mb, 34, bb‘), 
which is the direct continuation of the cellular matrix of the in- 
tegument and exteriorly to this by a particularly strong muscular 
investment. This muscle is apparently a local differentiation of 
the pair of ventral longitudinal muscles, and along its ventral sur- 
face still in connection with these. Its fibres are no not strietly 
longitudinal but partly radially inserted, being interwoven in 
various different directions. 
Closer investigation shows that all the constituents together are only 
present in the anterior portion ofthe apparatus, furthest removed from 
its opening to the exterior. It first appears as a local thickening and 
separation of the muscle extending below the ducts RR (fig. 31, 32). 
In following sections a cavity originates inside this longitudinal 
musele and attains an increased diameter in each of the consecutive 
sections. This is the cavity lined by the cellular layer above men- 
tioned and filled with the curious contents. Some twenty sections 
further on the muscle does not surround it any more on all. sides 
but on one side the cellular coating forms the limit. This dis- 
