40 THE VOYAGE OF H.M.S. CHALLENGER. 



and that tlieir properties can be studied -^-ith success only in the living state. The 

 constituent parts of the mesoderm are as usual represented by a transparent ground- 

 mass, by stellate or fusiform cells and cellular elements of amoeboid character. The 

 amoeboid cells differ from the first-mentioned apart from their general shape by their 

 nucleus being comparatively larger. It is generally accepted that the amoeboid cells 

 in the sponges give origin to the generative products ; both the specimens of 

 lanthella proved, however, to be sterile ; in one of them, indeed, I found here and there 

 large egg-shaped bodies, but since I did not succeed in discerning in them anything like 

 a nucleus, I am far from being sure whether they were really ova or something else. 

 The stellate mesodermic cells, as well as those of fusiform shape, do not differ from those 

 of Sycon rciphanus as described by F. E. Schulze,^ but it must be said that whUe their 

 fusiform modification is very seldom found in Sycon raphamis and the Calcarea generally, 

 it is far more common in lantheUa than the stellate form. Particularly near the outer 

 surfaces these fusiform, probably contractile, cells are very numerous, surrounding in rows 

 the pores and oscula (PI. II. fig. 6). I have spoken of them in their special modification 

 as spongoblasts before, and it only remains for me to mention the interesting hypodermic 

 elements, without entering upon the discussion of the question as to whether they are 

 really modified stellate and not amoeboid ceUs. At any rate they are larger than both 

 the stellate and the amoeboid ones, and their protoplasm is far richer in granules. It is 

 indeed difficult, when seeing these elements Ipng separately amid fusiform muscle-ceUs 

 (as drawn on PL II. fig. 6), to resist the idea that these elements are of a nervous nature, 

 and their histological properties, so far as they could have been studied from the material 

 preserved in alcohol, agree tolerably well with what we regard as tjrpical nerve-ceUs. I must 

 say, however, that I was unable to discern any connection between them and the fusiform 

 ceUs, and on the whole consider theu" nervous nature to be as doubtful as that of certain 

 mesodermic cells described by SoUas - in Tlienea muricata, as well as that of the anastomos- 

 ing " Strange " discovered by F. E. Schulze ^ in the Spongidse. I believe these cells to be 

 equivalent to the gland-ceUs stated by v. Lendenfeld * to be present in his South Sea 

 Aplysinidce, and five years before by Merejkowsky* in his Halisarca (Oscarellaf) scJmlzei. 

 I have found similar cells in Ajilysilla sulj)hurea and Darwinella aurea, and I am the 

 more inclined to compare the enigmatic elements of lanthella with these gland-cells, 

 since, as I remarked before, the external surfiice of this sponge is covered by a thin 

 cuticle. Of course they arc larger than common spongoblasts, whUe the gland-cells of v. 

 Lendenfeld agree mth these latter both in shape and size, but this difference seems to me 

 to be of no great importance. The best methods for rendering these, as well as hypo- 

 dermic fusiform cells, visible are eosine and gold, for which latter the alcohol must be 

 previously extracted. 



I Zeitschr.f. wiss. Zool., Bd. sxv., Suppl., p. 253. ^ /(,),;. and Mag. Nat. Hist, ser. 5, vol. ix. p. 44G. 



^ Zeitschr.f. wiss. Zool., Bd. xxxji. p. 629. ■* Ibid., Bd. xxxviii. p. 278. 



' Mem. Acad. Sci. St. Petersk, vol. xxvi. Xo. 7, pi. ii. fig. 9. 



