800 SUMMARY OF CURRENT RESEARCHES RELATING TO 



which evaporates in from 2-G days, according to the weather. In 

 the collected rain-water a characteristic fauna was found to exist, 

 notwithstanding the periodical desiccation. A peculiar variety of 

 Philodina roseola seemed to have grown up in that habitat, as well 

 as a Tardigrade, an Amoeba, Flagellates, a Stylonychia, Volvocineaa, 

 Heematococcus pluvialis, &c. Observations made nearly fifty years 

 ago indicate the presence at that date of a similar fauna, and there is 

 every reason to believe that at least for a century similar forms have 

 tenanted the cavity. Thus the fauna has persisted, in spite of complete 

 desiccation — thousands of times repeated. The problem is, how ? 



As the result of experiments, Prof. Zacharias found that specimens 

 of Philodina and Tardigrada, when allowed to dry, invariably died, 

 but that the ova were by encystation preserved from death by 

 desiccation. To the eggs, therefore, which develope with returning 

 rain, the " revivification " is wholly due. 



What has thus been shown in regard to the Rotatoria and Tardi- 

 grada has been demonstrated by Ilallez as to small Nematodes 

 (Rhabditis aceti), which were also credited with revivification. The 

 zygospore stage of Stephanosphsera and the resting stage of Hsemato- 

 coccus explain the persistence of these algoid forms in the pool ; while 

 the Am< rise and Flagellata doubtless adopt similar protective measures. 

 There is therefore probably no such thing as a real fauna and flora 

 rediviva. 



Prof. Zacharias further notes how the selective process has resulted 

 in the development of a special variety of Philodina (P. cinnabar in< % ) 

 of large size, bright colour, and bolder habit, resulting from the 

 absence of enemies. 



Development of Balanoglossus.* — Mr. W. Bateson continues his 

 account of the development of Balanoglossus Kowalevskii, and has 

 some notes on B. sahnoneus and B. robinii from Brittany. The skin 

 is ciliated, and the long cells of which it is composed regularly 

 anastomose with one another, so that the surface of the skin is made 

 up of a sort of honeycomb of tissue, each of whose nodes is the outer 

 end of an ectoderm cell. Inferiorly each cell is continued into a 

 long and very fine filament, which may be followed into the layer of 

 nerve-fibre, which is always more or less developed at the base of the 

 ectoderm-cells over the whole body. Teased preparations always 

 reveal the presence of large spindle-shaped cells, which appear to be 

 broken off from the ends of the long ectoderm cells, and not to be the 

 elements of a second layer. The resemblance between the skin of 

 Nemertines and that of Balanoglossus is very close. Nerve-fibres 

 of ectodermic origin are present in abundance, and appear to be 

 motor nerves ; the concentration of the nerve-fibres is most marked 

 in the region of the collar. The skin covering the liver-saccules is 

 very thin, and in B. sahnoneus is often fused with the hypoblast, 

 forming openings which place the cavities of the hepatic diverticula 

 in actual connection with the exterior. 



The radial muscular fibres are much more common in B. sahnoneus 



* Quart. Journ. Micr. ScL, xxvi. (1SSG) pp. .~>1 1 — :; 1 (G pis.). 



