146 



SCIENTIFIC NEWS. 



[Aug. 17, li 



exchanging the dark-chamber water with that in the 

 show tanks, and partly by jets of water carrying down 

 adhering air into the tanks. 



I may here remark, by the way, that air may be more 

 effectively injected into an aquarium thus, than by forcing 

 jets of mere air itself. The jet of air forms comparatively 

 large bubbles, but the jet of water carries down with it 

 a cloud of bubbles so minute that they expose a far larger 

 surface, and rise but slowly through the water. The 

 water jet should start from its nozzle at a very short 

 distance above the surface of the water, a distance vary- 

 ing with the size and force of the jet. This can easily be 

 tested by observing the dimensions and character of the 

 cloud of bubbles produced. 



Applying these experiences to the case of the Lake of 

 Geneva, the explanation is obvious. In the summer the 

 upper part of the blue water is made turbid by microscopic 

 vegetation, which in the winter has little or no existence. 



While Lloyd was making his experiments with shaded 

 tanks and dark reservoirs, I was attacking the same 

 problem chemically, and found that when the sea water 

 thus became turbid it simultaneously became faintly 

 alkaline. This I attributed to the removal of carbonic 

 acid from the sea water, and the precipitation of some of 

 the carbonate of lime that is present in all ordinary sea 

 water, and is dissolved in excess of carbonic acid. This 

 precipitation of course increased the turbidity. 



To test this theory, I added, very cautiously and gradu- 

 ally, small quantities of hydrochloric acid. This effectually 

 restored the transparency of the water, but did not meet 

 with the approval of the animals. The actinia closed 

 and became conical, and fishes were seized with fits of 

 coughing, especially when I substituted chlorine-water, or 

 bromine solution (both of which cleared the water) for 

 hydrochloric acid. 



A serious trouble arose at the opening, or rather in- 

 tended opening, of the Crystal Palace aquarium. This 

 was announced for Easter Monday. The tanks and 

 underground reservoir, and duplicate pumping machin- 

 ery were all punctually ready, and the sea water in its 

 place, but although clear when poured in became quite 

 milky in a very short time, and all the first stock of 

 animals perished. At Mr. Lloyd's suggestion I was con- 

 sulted by the manager, and soon discovered the cause. 

 The water was alkaline, the alkalinity was due to caustic 

 lime in solution, the caustic lime came from the Portland 

 cement with which the underground reservoir was lined, 

 and by which the rockwork of the tanks was held. Two 

 courses were open for the remedy of this. One was 

 heroic, the other cautious. The heroic remedy was to 

 add sufficient hydrochloric acid to neutralise the dissolved 

 lime, and to dissolve the precipitating carbonate; the 

 prudent course was to go on circulating the water until 

 the carbonic acid of the air gradually did the work. I 

 proved the possibility of clearing at once by an experi- 

 ment in an isolated single tank, but Lloyd had a dread of 

 mysterious chemicals, and preferred the cautious course, 

 which was carried out, but demanded a long time, and 

 the opening of the aquarium was postponed accordingly. 

 The complete success of this justified Lloyd's selection. 



«->»^<^5«C^ 



Influence of Trees on the Rainfall. — The re- 

 forestation of portions of North-western India is already 

 exerting a beneficial influence by an increasing rainfall 

 in the Southern Punjab, Southern Afghanistan, Northern 

 Beloochistan^and Northern Scinde. 



THE NATURALIST AT THE SEA-SIDE. 



V. — Some Marine Larv.£. 



'"THE larvae of which we have to speak are the Ascidian 

 Tadpoles, and the tiny creature long known as Acti- 

 notrocha, which turns out to be the immature state of the 

 worm Phoronis. If the reader will forgive the alarming 

 names which these minute and fragile animals bear, he 

 will find that their acquaintance is well worth making. 

 The Ascidian Tadpole is especially noteworthy in this, 

 that while it resembles in nearly all essentials the more 

 familiar tadpole of the frog and toad, it is destined to be 

 transformed into something entirely unlike any amphi- 

 bian, viz., a fixed and rooted leather-coated sea-squirt. 

 Actinotrocha has something of the same peculiar interest, 

 resembling as it does the larvae of animals extremely 

 different in the adult condition, such as echinoderms, 

 various worms, and some mollusks. It exhibits a 

 singular mode of transformation adapted to its own 

 special needs, and unexampled in certain respects among 

 other living things. 



The Ascidian Tadpole is to be found swimming near 

 the surface of the sea in bright summer weather, and is 

 often taken in the tow-net. It is a small reddish animal 

 easily seen by the naked eye, but requiring a microscope 

 for anatomical examination. When the muslin of the 

 tow-net is washed out in a glass dish, the Ascidian Tad- 

 poles are at once identified by their rapid and peculiar 

 movements. Pick them up with a dipping-tube and 

 transfer them to a preservative fluid, when the details of 

 their organism can be made out. 



Like the tadpole of the frog the ascidian larva has a 

 swollen "head" and a long swimming tail. The "head" 

 in each animal is provided with paired slits by which 

 the water taken in by the mouth passes out. The slits 

 do not open directly to the exterior in the ascidian, but 

 lead into a chamber which has its outlet in a spiracle at 

 the back of the head. The tadpole of the frog exhibits 

 precisely the same arrangement after the earliest stages 

 of its free existence are past. Then there is a solid 

 flexible fibre in the young ascidian, which agrees both in 

 structure and position with the very similar notochord 

 of the amphibian tadpole; the nerve-cord is almost 

 identical in the .two types, and both have the peculiar 

 " cerebral " eye with rods and cones pointing inwards, 

 and adapted to the reception of the rays of light received 

 through the transparent brain. 



The resemblances between the two sorts of tadpole 

 are therefore by no means superficial, but extend to the 

 most characteristic features of vertebrate organisation. 

 The line once drawn so boldly between vertebrates and 

 invertebrates is effaced by the Ascidian Tadpole, and for 

 this reason, if for no other, our restless little larva is. 

 worth the most serious attention. 



After its short term of activity comes to an end, the 

 larva attaches itself by papillae (which find their equiva- 

 lent in the suckers of the amphibian tadpole), the tail is 

 absorbed ; some organs degenerate, while others become 

 immensely developed ; and what bade fair at one time 

 to become an active, powerful, and intelligent vertebrate, 

 sinks into a motionless sea-quirt with capacious mouth, 

 stomach, and intestine, a stift and insensitive skin, and a 

 mere ganglion in place of brain and spinal cord* . 



Actinotrocha is a very minute creature, just visible as 

 a moving speck in surface collections. A lens or micro- 



* A very interesting popular history of the Ascidian Tadpole is. 

 given in Lankester's "Degeneration." 



