NATURE 



393 



THURSDAY, AUGUST 



JAPANESE SPONGES. 

 Studies on the Hexactinellida. Contribution I. (Euplec- 

 tellida;). By Isao lijima. Pp. 299 ; 14 plates. 

 (Reprinted from ■Cae. Journal of the College of Science, 

 Imperial University, Tokyo, Japan, vol. xv. 1901.) 



THIS important memoir is the first instalment of a 

 general monograph of the rich Hexactinellid fauna 

 of the Japanese seas, upon the study of which the author 

 has been engaged for the last seven years, with the result 

 of increasing very largely the list of these interesting 

 and beautiful sponges known to occur in that part of the 

 world. Four species of Euplectella, three of Regadrella 

 and one of IValleria are here described in great detail, 

 and all but two of them are species described and named 

 by the author himself, either in previous publications or 

 in this memoir for the first time. The part of the work, 

 however, which above all claims the attention of the zoo- 

 logist who is not specially interested in this group of 

 animals, or in the faunistic problems which attach to 

 them, is the detailed account of the histology and organi- 

 sation of Euplectella marshalli (pp. 116-200). The 

 author has had at his disposal a very abundant material 

 of this sponge, which he was able to preserve by various 

 methods directly after capture. As the result of his 

 careful studies upon this valuable material, the author 

 describes in these Hexactinellids a type of structure 

 which is radically difierent in two main points from that 

 of all other sponges, and in both respects probably to be 

 regarded as more primitive. 



In the first place, he finds no trace of the intercellular 

 matrix ormesogloeaof the connective tissue parenchyma, 

 which in other sponges forms the chief mass of the 

 sponge body. In the second place, perhaps in conse- 

 quence of the absence of any such ground substance, there 

 is no layer of fiat epithelium to be found on any part of 

 the sponge body, neither on the external surface nor in 

 the canal system. 



The dermal layer, in short, forms in these Hexactinellids 

 a system of trabecuke, composed of fused cells corre- 

 sponding to the coUencytes of other sponges, which here 

 form a continuous protoplasmic syncytium with scattered 

 nuclei. In this syncytium the spicules are laid down, 

 but there is no secreted matrix apart from them and from 

 the protoplasm of the syncytium, nor is there any flat 

 epithelium covering the exposed surfaces. The trabe- 

 cula- anastomose and form a cobweb-like felt-work, 

 through which the water filters both before and after 

 traversing the flagellated chambers. .A.t the e.xternal and 

 . internal surfaces of the body wall the trabecular are 

 expanded to form film-like membranes perforated by 

 numerous gaps or pores, the so-called dermal and gastral 

 membranes. In the trabecular system are found other 

 cellular elements, the arch.eocytes, with their modifica- 

 tions into nutritive and reproductive elements. 



If the author's observations are confirmed, therefore, 

 the Hexactinellids stand on a lower plane of evolution, at 

 least as regards histological structure, than any other 

 sponges, in that the dermal layer forms only one category 

 of cell elements and is not differentiated into separate 

 NO. 1660, VOL. 64] 



epithelial and connective tissue strata. This conclusion, 

 it is hardly necessary to point out, is in direct antagonism 

 to the view, still maintained by many authorities, accord- 

 ing to which these two commonly found differentiations 

 of the dermal layer are to be regarded as an "ectoderm •' 

 and a "mesoderm" respectively. In the author's words, 

 the Hexactinellids "are a group of sponges which have 

 undergone a far-reaching development and differentiation 

 in the spicules, but have remained in a primitive condi- 

 tion so far as certain points in the soft parts are 

 concerned." 



The author has also made a number of important 

 observations upon other points of microscopic structure. 

 He brings forward the first observations yet made upon 

 the formation of spicules in these sponges. He has also 

 observed "archseocyte congeries" which he believes to 

 give rise to free larvae, thus reverting to, and supporting, 

 the view of H. V. Wilson, that many sponge larv;e 

 are really free-swimming gemmules, and are not egg- 

 larva;. But the account given of the collar cells and 

 flagellated chambers merits special mention, as differing 

 in some points, both important and unimportant, from 

 Schulze's recently published description of the collar 

 cells in another Hexactinellid, 5c7/^!«r//«;//rt arctica. Each 

 collar cell has a flattened basal portion containing the 

 nucleus and running out into ramifying processes, which 

 anastomose with those of neighbouring cells to form the 

 "reticular membrane " of Schulze. According to lijima, 

 all the meshes of the reticular membrane are open and 

 serve as prosopyles or chamber pores, which are there- 

 fore practically equal in number to the collar cells them- 

 selves, " converting the epithelium into a veritable sieve 

 membrane." The trabecule of the dermal layer attach 

 themselves directly to the reticular membrane. The 

 " polyprosopylar '' condition here described contrasts 

 sharply with what is seen in other sponges, and in the 

 author's opinion it is correlated with the absence of 

 mesogloea. In sponges other than Hexactinellids, i.e. 

 in Calcarea and Demospongix, the copious deposit of 

 the ground substance round the bases of the collar cells 

 necessarily blocks the free infiltration of the water between 

 them, and causes a specialisation of the prosopyles ; 

 they become few in number and restricted in distribution, 

 while between them the collar cells close up their ranks 

 and extinguish the gaps in the wall. In Calcarea at 

 least, it may be added, the prosopyles are further 

 guarded, each by a special cell or porocyte of the dermal 

 layer. These porocytes have not as yet, however, been 

 demonstrated to occur in Demospongia;, and their 

 existence in Calcarea is, perhaps, a peculiarity of this 

 group alone. 



The histological facts brought forward by the author 

 throw a flood of light upon tlie nature of the prosopyles 

 or primitive pores of sponges, and if carried back in 

 imagination to the primitive vase-like Olynthus form, 

 which was probably the ancestor of all sponges, they 

 permit of interesting speculations as to the probable 

 structure of the body wall in such a form. The earliest 

 type of sponge must be pictured as entirely without 

 mesogtea, and with a thin basket-like wall perforated by 

 very numerous pores or interstices, corresponding to the 

 intervals between the collar cells. The first advance to- 

 wards strengthening this fragile structure would have 



