NARRATIVE OF THE CRUISE. 
641 
particles, -he regards as a necessary result of such a kind of growth the substitution 
of pavement epithelium for flagellated epithelium covering the central cavity in the 
Olynthus, as well as the formation of differentiated flagellated chambers (radial 
tubes).. In harmony with all this, and since, through forms like Leucilla liter, 
Leucilla connexiva, Amphoriscus elongatus and Amphoriscus poculum, the typical 
Sy con idee are most closely connected with typical Leuconidse, Dr. Polejaeff upholds 
the existence of an absolute distinction between the Asconidse and all other Calcarea, 
and gives systematic expression to it by subdividing the group into two orders. 
“ Although the above theory is regarded as quite plausible, it must however be 
noticed that it stands in a certain contradiction to some embryological data which, 
though mentioned by the author, are not brought into harmony with his hypothesis. 
Polejaeff regards his Homoccela and Heterocoela as systematically equivalent groups, i.e., 
to present divergent branches from the same spot of the genealogical tree of the animals. 
Again, on page 21 of his Memoir, he adopts the opinion upheld by Metschnikoff that 
in Parenchymula we have to do with a larva of more primary characters than those of 
Amphiblastula, both these larvae, as is well known, being characteristic of the Calcarea. 
But it is also known that these larvae are not distributed in such a manner that 
Parenchymula characterises the development of Homocoela and Amphiblastula that of 
Heterocoela. The latter is of course true, but the development of Homocoela is charac- 
terised in some instances by Parenchymula, in others by Amphiblastula. The contra- 
diction above alluded to is clear. And it is equally plain that the hypothesis under 
consideration will become theory only when it has been proved either that the statements 
of Barrois and Keller as to the occurrence of Amphiblastula within the Asconidse are 
based on a mistake, or that the opinion of Metschnikoff above mentioned is erroneous, or 
finally that the Amphiblastula of Heterocoela and that of Homocoela are only analogous 
and not homologous larvae. 
To return to the results of the Eeport, which concern the Heterocoela almost 
exclusively. As to the order of Homocoela, the author believes it to contain only a 
single family, but he is not prepared to say whether this family consists of but one or 
of many genera. On the whole he believes our knowledge on this head to be still very 
deficient. 
“ In the order Heterocoela three families are distinguished, all already established by 
former systematists. The inducement to adopt the family Teichonidae established by Carter 
for a single genus, Teichonella, has been given by the circumstance that the Challenger 
collection contained a form, the beautiful Eilhardia schulzei (see fig. 218), with its silvery 
lustre, which, closely allied to the genus Teichonella as it is, differs from it so very much 
that the creation of a new genus, and thus the adoption of the whole family, became indis- 
pensable. The family is characterised by having the outer surface differentiated into two 
different planes, one bearing oscula, the other pores, and the internal organisation of its re- 
