16 REPORT—1852. 
they were drawn iato it, and carried through it by the action of the cilia lining the 
interior, and were then ejected and borne off by the tentacular currents. This ex- 
pulsion went on for three or four minutes, during which time the active filaments 
were streaming up from the lower part of the cell. After awhile a single sperma- 
toxoon only made its appearance occasionally, and at last none were to be seen. The 
ciliated intertentacular organ, then, communicates with the visceral cavity, and is at 
certain seasons the channel through which large quantities of Spermatozoa are ejected 
and diffused through the surrounding water. 
Similar observations were made on the Cycloum. I have never met with Sper- 
matoxoa in any individual which was not provided with the organ (and I have ex- 
amined hundreds), while in those which possessed it, they were frequently present 
at the proper season in astonishing profusion. The organ occurs on comparatively 
few individuals. This has been ascertained by a careful examination of great numbers- 
at different seasons of the year. 
With the facts now related before us, there can be little doubt that the interten- 
tacular organ of the Membranipora, Aleyonidium, and Cycloum marks a difference of 
sex. It characterizes the male individuals, and is aspecial provision for the expulsion 
of the Spermatozoa, which are produced in great profusion in a few of the cells, and 
being thence diffused through the surrounding water, are drawn in by the tentacular 
currents of other individuals (female), and so fertilize the ova. 
A separation of the sexual organs has also been observed in some of the freshwater 
Bryozoa, but I am not aware that any of the latter are supplied with the interten- 
tacular organ. 

—_— 
Researches into the Structure of the Ascidians. 
By Tuomas H. Huxtey, F.R.S., Assist. Surgeon R.N. 
The author stated that he was desirous of laying before the Section an account of 
some investigations into the structure of the Ascidians which he had been led to 
make while endeavouring to form a catalogue of those contained in the collection of 
the British Museum. 
The Ascidians, varied as they are in external appearance, present certain general 
anatomical uniformities, which are capable of being represented by a diagram. To 
such a hypothetical structure thus represented, the author gives the name of the 
Archetypal Ascidian. From this every actual form can be shown to be derived, by very 
simple Jaws of modification. The author particularly desired it to be understood 
that he attached no other meaning to the term Archetype than that thus defined. 
It has been a matter of dispute which is the dorsal and which the yentral side of 
the Ascidians ; there can be no question, however, that the heart is upon one side of 
the axis of the body, and that the nervous ganglion is upon the other ; to avoid all 
ambiguity therefore, the author proposes to speak of the ‘‘ hemal” and of the 
“neural” eides, in accordance with the nomenclature proposed by him in a 
memoir ‘Upon the Homologies of the Mollusca,’ read before the Royal Society. 
The Ascidian Archetype differs from all others in the following points : 
1. The intestine is always flexed towards the hemal side. In the Polyzoa it is 
flexed towards the neural side, as pointed out by Professor Allman. . 
2. The tentacles are small, while the pharynx is very large, and serves as a respi- 
ratory cavity, its parietes becoming perforated. The author combated the view that 
the “‘ branchial sac”’ of the Ascidian answers to the tentacles of the Polyzoon, or to 
the united gills of the Lamellibranchiate Mollusk ; in opposition to the former view, 
he endeavoured to show that the tentacles of the Polyzoa are represented by the 
tentacles of the Ascidians; and against the latter, he urged, that the gills of the 
Bivalve Mollusk have no representative in the Ascidian. The “ branchial sac ” of 
the latter, represents not the gills of the Mollusk, but the perforated pharynx of 
Amphioxus ; an analogy which has already been noticed by many observers. 
The author brought forward the structure of the peculiar genus Appendicularia, 
as fatal to the view that the branchial sac of the Ascidian is homologous with the . 
united tentacles of the Polyzoa. 
Especial attention was directed to the formation of what the author termed the 
“ Atrium,” under which term he included the cloaca and the space between the 
branchial sac and the ‘‘ third tunic ” of writers, The author endeavoured to show 
