ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
585 
Molluscoida. 
a. Tunicata. 
Classification of the Tunicata.* — Prof. W. A. Herdman has an essay 
on the classification of the Tunicata in relation to evolution. The 
exceptional diversity of opinion exhibited by systematists is probably 
due to the complex relations which obtain between the compound 
forms and the other Tunicata. He thinks that the only rational expla- 
nation of the protean forms and labyrinthine interrelations of the Asci- 
dians is to be found in regarding the group as one in process of evolution, 
where many species, genera, and higher divisions have not yet become 
markedly differentiated by the elimination of intermediate forms ; he 
thinks, moreover, that the animals are so much at the mercy of their 
environment that a special premium is set upon useful characters, so 
that the relations between modifications of structure and conditions of 
existence brought about by the action of natural selection are excep- 
tionally evident. 
The author becomes more and more convinced that it is necessary to 
regard the compound Ascidians as having had a polyphyletic origin, and 
to represent the group as linked on to the Ascidise Simplices by at least 
three points ; moreover, if we attempt to arrange the families and genera 
in a series diverging from any one of these points alone, we must not be 
surprised if we arrive at obviously unnatural arrangements. 
Prof. Herdman points out various objections to the scheme of classifi- 
cation lately propounded by M. Lahille, and urges that if the use of 
the modifications of structure of one organ are especially unsafe, it is 
the more so when, as in this case, the organ (the branchial sac) is of 
great physiological importance, and is therefore liable to be considerably 
modified in accordance with the mode of life of forms which are otherwise 
closely related. 
Some interesting details are given as to the variation exhibited by 
the Botrylli , and the author concludes with pointing out that the theory 
of evolution has given taxonomy and speciography an additional and a 
very real interest. We know now just how much and how little the 
term species indicates, and it has, therefore, become of great importance 
that species and varieties should be restudied from the evolutionary 
standpoint, that the relations of allied forms should be carefully in- 
vestigated, the limits of their variation determined, and the effect of their 
environment ascertained. 
&. Bryozoa. 
Loxosoma annelidicola.f — Dr. H. Prouho gives a detailed account 
of this Bryozoon, to the preliminary notice of which we have already 
called attention.]; The creature varies from 35 to 80 hundredths of 
a millimetre, and its integument is colourless. In this integument 
there are no glandular cells. The stalk ends in an adhesive disc which 
may attain considerable size, but there is no trace of the pedal gland 
which has been seen in other members of the genus ; nor is there need 
of one, for the disc can act as a sucker. The arrangement of the 
muscles of the stalk is such that the animal is enabled to rotate on its 
* Nature, xliv. (1891) pp. 130-3. 
t Arch. Zool. Exper. et Gen., x. (1891) pp. 91-116 (1 pi.). J Vide ante , p. 29. 
