EEPOET OE" THE TUNICATA. 
35 
Lamarck^ in 1815 formed the genus Polycyclus for a Botrylloid species producing a 
thick fleshy colony. This genus was not recognised by Savigny, who in 1816^ divided the 
single genus Botryllus into two sections : — (1) “ Botrylli stellati” having the Ascidiozooids 
of each system placed in one row, and (2) “ Botrylli congiomerati,” where the Ascidio- 
zooids form several rows. The latter included only one species, Botryllus conglomeratus, 
Gaertner, said to be found on the English coast. There is considerable doubt as to this 
species. Possibly it does not belong to the Botryllidse.^ Savigny further divided the 
Botrylli stellati into — (1) those where the Ascidiozooids are cylindrical and have the 
branchial and atrial apertures close together, and where the margin of the common cloaca 
is not distinct ; and (2) those where the Ascidiozooids are ovoid and have the apertures 
distant, and where the margin of the common cloaca is always visible. This was a very 
natural classification, and it has been upheld by almost every writer on the Botryllidse 
Fig. 7. — A Colony of a Compound Ascidian {Botryllm). The Ascidiozooids are arranged in eight systems. 
a, a large system formed of fifteen A.scidiozooids ; b, a small system formed of seven Ascidiozooids ; c, the test or invest- 
ing mass ; d, a common cloacal aperture ; e, an Ascidiozooid ; /, the terminal knobs of the vessels ; g, a system 
where the common cloacal aperture is fully expanded. 
since. Milne-Edwards recognised the value of the distinction, and in 1841'* raised the two 
groups to generic rank by founding the new genus Botrylloides for Savigny ’s first tribe 
of species ; Botryllus being restricted to the second series of forms. As Giard and others 
have pointed out, these two genera differ not only in the shape of the Ascidiozooids and 
in the common cloacal aperture, but also in the shape of the systems composing the 
colony (compare Fig. 7 with Fig. 8, D and E, p. 39). 
Della Valle® showed in 1877 that Lamarck’s old genus Polycyclus, which, although it 
had been employed by some authors {e.g., Eisso,® Delle Chiaje,^ and Grube’^), was by no 
1 M^m. Mus. Hist. Nat. Paris, t. i. p. .340. ^ Memoires sur les Anim. sans Vert. 
3 From the description and figure given by Pallas (Spicilegia ZooL, fasc. 10, Berolini, 1774, p. 39, Tab. iv. fig. 6) 
it is evident that the animal in question is a Compound Ascidian ; it is, however, impossible to say with any certainty 
even the family to which it belongs. The figure seems to me much more like one. of the Polyclinidae than one of the 
Botryllidre. It is not unlike a small colony of Amaroucium proliferum. Consequently, I think Savigny’s second section 
may be regarded as having been probably founded upon a mistaken identification, and may now be suppressed. 
* Observations sur les Asc. Comp., &c. « Contrib. alia Storia Nat. d. Asc. Comp., &c., p. 22. 
® Mem. Mus. Hist. Nat. Paris, 1826, t. iv. p. 280. ’’’ Descriz., &c,, vol. iii. p. 19. 
* Die Insel Lussin, &c., p. 64, Breslau, 1864. 
