30 THE VOYAGE OF H.M.S. CHALLENGEE. 



proceeding would have been as natural and comprehensible bad it taken place before the 

 classical investigations of F. E. Schiilze were published, as it is strange'now, Dr. Marshall's 

 paper in question having been issued in the year 1881. Dr. Vosmaer^ places this genus 

 in his and F. E. Schulze's family Hircinidse, another proceeding which would be quite 

 inexplicable, since the species of Oligoceras hitherto described is entirely devoid of any 

 filaments, had it not a very simple explanation, that of an erratum. Schulze himself lays 

 great stress on the close affinity of Oligoceras with Cacospongia, and indeed, since in its 

 somewhat absolute character (I speak of that of the canal system) the genus thoroughly 

 agrees with other Spongidse, and differs from Cacosjpongia only by secondary and therefore 

 extremely conditional characters, its natural systematic place is near Cacospongia. The 

 differentiating characters above mentioned are the foUov/ing : (l) the tendency to take 

 foreign bodies into the parenchyma, and particularly on to the external surface ; (2) the 

 want of a proper network of horny fibres, the horny substance being developed so scantily 

 that portions of the body as large as peas are completely devoid of any skeletal fibres ; 

 (3) the structure of the skeleton, its fibres being overcharged with foreign enclosures, 

 and the skeleton on the whole being represented by isolated fibres which have only rare 

 anastomoses and ramify widely like the antlers of a stag. Do these characters together 

 justify the estaljlishment of a genus, even from the naturalist's point of view, not demand- 

 ing for generic distinctions differences of an absolute nature 1 I see, logically at least, 

 no grounds for answering this question in the negative, since one may regard the 

 Oligoceratidse as a group of forms with a tendency to lose the horny skeleton entirely 

 in order to become Myxospongida3, or at least analogues of Psammopemma among the 

 Spongidse. Oligoceras has accordingly the same right to exist as a genus as Cacospongia 

 or Hippospongia, each personifying a new principle, all being connected amongst them- 

 selves by all possible intermediate stages. From this point of view I should be obliged 

 to adopt F. E. Schulze's genus in question ; I cannot, however, do so on account of the 

 unusually conditional nature of the characters distinguishing the Oligoceratidse, apart 

 from the point that the transformation of a true Cacospongia into a not less typical 

 Oligoceras appears to be very easily realisable (eomp. p. 84). The characters separating 

 Cacospongia and Euspongia from one another are also conditional, but in this latter case 

 at least a conventional boundary is admissible. We can, if necessary, group in Euspongia 

 forms with fibres not thicker, and with meshes not larger, than a given dimension, the 

 forms with larger meshes and thicker fibres being grouped in the genus Cacospongia. 

 But even a similar, quite artificial boundary is not applicable to the distinctions between 

 Cacospongia and Oligoceras. All Spongidje take foreign bodies into the parenchyma as 

 well as into the skeletal fibres, and F. E. Schulze " himself warns us not to ascribe to this 

 character too great a significance. But apart from this, even did the taking in of foreign 

 bodies represent the manifestation of an " unknown intellectual power," and were their 



' On Velinea gracilis, p. 445. • Zeitschr.f. wiss. Zool., Bd. xxxiii. p. 14. 



