THE VOYAGE OF H.M.S. CHALLENGER. 



B. Embryological Notes. 



We had. at first intended to give a somewhat detailed account of a mimber of embryos 

 which we have met with in the course of our work, but after consulting the literature ^ 

 bearing upon this much vexed portion of our subject, we have decided that it is desirable 

 to say as little as possible. There are already so many contradictory ojiinions with 

 regard to the development of the sponges, and, according to Heider, it is so extremely 

 unsafe to draw conclusions from specimens that have been preserved in spirit, that, for 

 fear of adding to the ah-eady existing confusion, we naturally feel very diffident about 

 recording our observations ; we shall, therefore, make our remarks on this head very 

 short. 



Concerning the position in which the embryos develop in the sponge, the most 

 interesting point seems to be that, as might be expected, they always develop in the 

 position of greatest security. In large, massive sponges it is obvious that, so long as they 

 do not lie very near to the surface, the position is a matter of no very great importance, and 

 accordingly in Esperella lapidiformis, e.g. , we find them scattered through the choanosome 

 in groups, commencing a short distance below the surface of the sponge (PI. XVI. fig. 2a, e). 

 In smaU and delicate species, however, the position becomes a matter of considerable 

 importance ; thus in Esperella hiserialis, where the sponge consists of a central spicular 

 axis coated by only a thin layer of soft tissues, we find the embryos (PI. XIV. fig. 3, e) 

 taking refuge in the centre of the spicular axis. Again in Esperella mammiformis, a 

 hemispherical sponge (PL XIV. figs. 5, 6) with flat base attached to stones, the embryos 

 are found grouped close to the stone near the centre of the base. In Chondrocladia 

 crinita, a "Crinorhiza" form (PI. XX. fig. 4), the embryos again occur in the soft 

 tissues near the centre of the sponge, and each appears to be surrounded by a dense mass 

 of the characteristic isochelse of the species. 



The ova are, of course, developed from amoeboid mesodermal cells, and it appears 

 from our observations on Esperella lapidiformis {vide p. xxxi) that they may originate 

 either in the choanosome or the ectosome (the latter being gelatinous), but that they 

 develop only in the choanosome, whither we must imagine that those which originate in 

 the ectosome migrate. The free-swimming larva escapes from the parent sponge through 

 the exhalent canals, as is well shown in some of our preparations of Esper-ella murrayi 

 {vide PI. XLVIII. fig. 2, e). 



The commonest type of embryo met with by us is that R'hich occurs in Esperella 



1 Gf. Carter, Development of Marine Sponges, Ann. and Mag. Nat. Hist, ser. 4, vol. xiv. p. 321, et seq.; Keller, 

 Studien tiber Organization u. Entwickelung der Chalineen, Zeitschr. f. wiss. ZooL, Bd. xxxiii. p. 317 ; Marshall, 

 Die Ontogenie von Reniera filigrana, Zdtschr. f. iviss. Zool, Bd. xxxvii. p. 221 ; Schulze, Die Faniilie der 

 Spongidte, Zeitschr. f. wiss. Zool, Bd. xxxii. p. 593 ; Sollas, On the Development of Halisarca lobularis, Quart. 

 Journ. Micr. Sci., K.S., vol. xxiv. p. 6U3 ; Heider, Zur Metamorphose der Oscarella lobularis, Arb. zool. Inst. Wien, 

 Bd. vi.. Heft 2, p. 175 ; &c. 



