1883.] 



MICROSCOPICAL JOURNAL. 



209 



thought a few words about them might 

 interest some of tlie members of the 

 Quekett Club, ahhough I know the 

 two British species have been ably 

 treated by Mr. Waller. 



I shall not enter into the general 

 structure of the different species now 

 known, but confine myself to the stato- 

 blasts of the typical specimens of each 

 genus, noting any particular deviation 

 of form that may occur as we proceed, 

 and mentioning any peculiarity in the 

 form of those sponges in which the 

 statoblasts are unknown. 



The fresh-water sponges were first 

 made known as far back as 1696, and 

 in 1745 Linnajus described two spe- 

 cies under the respective names of 

 Spfl/ii^ia /firi'iati/is and Spongia lacus- 

 tris^ mentioning at the same time the 

 presence of the small seed-like bodies 

 generally associated with them. 



These organisms have been named 

 by different writers on the subject at 

 various times, gemmules, ovules, 

 ovisacs, spherules, capsules, and lastly 

 statoblasts or winter eggs, from their 

 close resemblance to the statoblasts 

 of the fresh-water bryozoa, not only in 

 outward appearance but also in their 

 being, according to Mr. Carter, simi- 

 lar in general internal structure, the 

 difference being only in size and form, 

 in having spicules instead of tentacu- 

 lar appendages on their surface, and 

 in the mode of discharging their con- 

 tents when matured. 



Now, as there have never been any 

 forms found in the marine sponges at 

 all resembling the statoblasts found in 

 the fresh-water sponges, a sharp line of 

 demarcation between the two is here 

 indicated by that circumstance alone. 



The reason assigned for the Stato- 

 b'asts occurring only in the fresh-water 

 and not in the marine sponges is, that 

 the former is often left high and dry 

 for weeks, perhaps for months together, 

 whilst the sea is constantly returning 

 to cover the latter, they therefore do 

 not require the protection to the ova 

 from the influence of the atmosphere 

 and other causes that the fresh-water 

 sponges would do. 



The statoblasts may be found most 

 abundantly at the base of the sponge 

 towards the autumn or winter, but in 

 the warm summer days they are plenti- 

 fully diffused throughout the entire 

 body of the sponge, excepting, per- 

 haps, quite the new growth. 



The late Dr. l^owerbank placed the 

 Spongilhi under the genus Isodidya on 

 account of the skeleton structure agree- 

 ing so perfectly in the form of the 

 spicules composing it, though distin- 

 guished from that genus by the pecu- 

 liarities of the reproductive organs, 

 viz., the statoblasts, the Spongilhi re- 

 producing its kind after the manner 

 of the marine sponges, that is to say, 

 by ova proper, and division of the 

 sarcode. 



The two British species were the 

 only ones known as fresh-water 

 sponges, until, in 1848 and 1849, Mr. 

 Carter published his interesting 

 " Memoirs on the Sponges found in 

 the Bombay Tanks," which memoir 

 will be found in the Annals of Natural 

 History of those dates. Since then 

 new forms and varieties have been met 

 with in Europe, Asia, and America, but 

 strange to say, none have as yet been 

 brought from Africa, although no 

 doubt they exist there. 



Describing the statoblast generally, 

 it is about the size of a large pin's 

 head, varying in this respect not only 

 with the species, but in the individual, 

 and can be seen with the unassisted 

 eye. In form it is more or less globu- 

 lar or oval, having a foramen or hilum, 

 either lateral or terminal on the sur- 

 face, generally at the bottom of an in- 

 fundibular depression which leads to 

 the interior. 



If we make a vertical section with 

 a sharp, thin knife, through the aper- 

 ture of one of these bodies when dry, 

 we shall observe that it consists of an 

 internal globular cavity, filled more or 

 less with a soft, waxy substance, of a 

 yellowish color, which substance, when 

 swollen out in water, will be found to 

 be composed of a great number of 

 thin, transparent sacs, somewhat 

 spherical, filled respectively with 



