1890.] A Zoblogical Reconnotssance. 435 
of the body narrows gradually to its so-called posterior end, 
throughout which it is covered with closely crowded, wen-like 
structures of a light pink color, The interior of this region of 
the body is dark purple, and there is, according to the notes, a 
terminal orifice (a). 
It will be noticed in reviewing Stimpson’s account, and com- 
paring his figures with those here published, that he also de- 
scribes two successive stages of development which correspond 
closely with those which I have figured. The “ tentacula” in 
the anterior region of one of those given are larger at the blunt 
extremity of the body, while the gonophores are in an advanced 
stage of development. In this stage of growth, organs which 
are called the “inferior appendages” by Stimpson had disap- 
peared. The stage last mentioned is supposed to be the adult, 
or at all events to be older than the other form which he figures. 
By comparing it with the adult of Myriothela, as figured ved 
Hincks and Allman, this conclusion seems to be tenable. 
If now we turn to the two similar stages shown in the figures, 
which we here have given, it will be found that the older (Fig. 
1), differs from the younger in the same way that the “ adult” in 
those by Stimpson differs from what he considers the young. 
Possibly the most important difference in each case between the 
two stages is the loss, in the adult, of the temporary tentacles 
found in the young. 
There have been several opinions expressed as to the relation- 
ships of the Acaulis. It has been called a free-swimming hy- 
droid, and associated with the supposed free hydroid of Nemop- 
sis, mentioned by McCrady. It has also been likened to a head 
of a Tubularian ruptured from a hydroid stem. The true affini- 
ties have been conjectured by several naturalists, but so little has 
been made known of the anatomy of Acaulis that it has been 
difficult to compare it with other hydroids. 
Hincks,’ in discussing the relationship of Acaulis and Myrio- 
thela, says “ Mr. Alder has suggested the probability of a close 
affinity between Myriothela and the Acaulis of Stimpson, and 
8 The young of Nemopsis has been shown to have a fixed hydroid. 
9A History of British Hydroids, pp. 76, 77 
