138 



SCIENCE. 



[Vol. XI. No. 26^ 



yet comparatively unknown. As far as has been ascertained, the 

 life-history of the Taenia pectinata is embraced in two stages. The 

 first covers the development of the ova into the embryo, which is 

 ready to leave the parent Taenia : the other covers the period of 

 growth from the youngest forms yet found in rabbits to the adult 

 stage. The life of the Taenia from the time they leave the first 

 rabbit as an embryo, until they are found as young Taenia in the 

 second rabbit infected, has as yet been unascertained. Among the 

 theories that have been advanced, is one that they pass this stage 

 upon the ground, are eaten by insects, snails, or crustaceans, and 

 that these are then eaten by the rabbits. This, however, is only a 

 theory, as none have ever been found in snails, insects, or crusta- 

 ceans. 



It was Mr. Curtice's good fortune to find a rabbit which had 

 recently been infeiJled with these peculiar parasites, none of which 

 were over three centimetres in length, many of them being less than 

 five millimetres long. There were more Taenia in that rabbit than 

 any he had ever seen before, — about eighty-five. Among the 

 smaller Taenia were several specimens that showed the stages of 

 development from non-segmented, armed forms, to segmented, un- 

 armed forms. Mr. Curtice showed to the society specimens illus- 

 trating the different stages. 



The youngest forms detected were not the smallest, but measured 

 about one-half a centimetre in length. They contained, in addition 

 to the four suckers, a cup-shaped cavity in the place of the rostel- 

 lum. Around the border of this cup-shaped cavity were situated 

 eighty-five or ninety hooks. The older specimens show a similar 

 cavity, with no hooks. Still older ones show no cavity at all. All 

 of these were in the non-segmented stages ; but other forms, some 

 of them smaller, were without signs of hooks, and had already 

 begun segmentation. 



Mr. Curtice compared these stages with similar stages in Taenia 

 Ji?ra/a, and said that the youngest stage of the Taenia pectitiata 

 was probably a cysticercoid stage, and not the cysticercal, and that 

 this was indicated by the cup-shaped cavity in the youngest forms 

 of the Taenia pectinata. 



In discussing the classification founded on the presence or ab- 

 sence of hooks, he declared it to be incorrect, since the discovery 

 described above shows that the unarmed species in adult stages are 

 armed in earlier stages. 



The speaker exhibited some elegant drawings made by Dr. 

 George Manx, illustrating the embryo as it leaves the parent Taenia. 

 This embryo is six-hooked, and surrounded by a curious pyriform 

 envelope, to which there is a double prolongation surmounted by a 

 cap of the same substance. The cap has a shredded border, and is 

 believed to be the remnants of a mass which, in an earlier stage, 

 completely surrounded the embryo. This peculiar envelope has 

 been previously noticed in Italy by Perroucito, and in France by 

 Raillet. This stage is similar to that found in Taenia expansa, the 

 unarmed tape-worrrrin sheep. 



Implanting Teeth. 



Dr. Yonger of San Francisco was the first dentist in this country 

 to perform successfully the experiment of implanting teeth. This 

 process is not to be confounded with transplanting teeth, which has 

 been practised by dentists for many years. In the latter operation, 

 a tooth freshly extracted is inserted in a socket from which one has 

 just been drawn, and the parts unite, circulation between the jaw 

 and the tooth is established, and the latter actually takes the place 

 of its predecessor. 



In Dr. Yonger's experiment, the tooth to be replaced has long 

 been extracted, and the socket filled up with bony substance. He 

 drills into the jaw, gouges out a new socket, and then, taking a 

 tooth that has long been extracted, cleans it thoroughly, soaks it in 

 bichloride of mercury, and inserts it in the socket just formed. 

 This new tooth in due time becomes firmly anchored, and as ser- 

 viceable as the original one before it became decayed. Dr. Yonger 

 holds that the tooth is held in its place by the soft tissues surround- 

 ing it, and that the artificial socket has nothing to do with anchor- 

 ing it. 



The experiment described above was performed by Dr. G. M. Cur- 

 tis of Syracuse, N.Y., who afterward extracted the implanted tooth, 

 and sent it to Dr. W. M. Gray, the microscopist of the surgeon- 



general's office, who has made a very careful examination of it. His- 

 experiments prove beyond question that the tooth so implanted is 

 revived, that circulation is established between the socket and the 

 implanted tooth, and that the socket does take an active part 

 in anchoring the tooth. A tooth so implanted is much more 

 firmly anchored in the jaw than one of the originals, and, in the 

 case referred to, the tooth was held so firmly that Dr. Curtis broke 

 it in extracting it. Dr. Gray does not doubt that the soft tissues 

 do take an active part in the operation, but he has proved his 

 propositions in regard to the bone and the tooth beyond all ques- 

 tion. 



Some Recent Discussions of Target-Shooting. 



At the last meeting of the Mathematical Section of the Philosophi- 

 cal Society, Mr. Charles H. Kummell read some remarks on some 

 recent discussions of target-shooting. In opening, he briefly re- 

 viewed a previous communication on the same subject which he- 

 had made in 1883, stating as the fundamental assumption (there 

 credited to Liagre, but due apparently to Poisson), that the devia- 

 tions of the shots from a vertical axis, called sighting errors, and 

 those from a horizontal axis, called levelling errors (each axis pass- 

 ing through the centre of the target), each independently follows 

 the exponential law of error. One of the most important conse- 

 quences of this assumption is, errors of shooting of equal proba- 

 bility are on the circumference of an ellipse whose axes are in the 

 ratio of the mean sighting and levelling errors. Among the 

 writers on the same subject, Mr. DeForrest, in the Transactions of 

 the Connecticut Academy, vol. vii. 1885, requires not only the 

 sighting and levelling axis, but even the centre of the target, to be 

 ignored, and a new centre and system of free axes determined 

 from the distribution of the shots on the given target. Mr. Kum- 

 mell thinks this method of discussion quite proper, if we really 

 were ignorant of the true position of centre and axes. But. such 

 not being the case, a merely probable thing should not be preferred 

 to a fact. 



In the January number of Comptes Rendiis, 1888, Mr. J. Bertrand 

 objects to the previous methods of discussing target-shooting, on 

 the ground that the levelling and sighting errors are not independ- 

 ent, but admits that in some as yet unknown curve (not an ellipse) 

 would be found shots of equal probability, and proposes to estab- 

 lish one of these curves for any given target by dividing it into a 

 convenient number of sectors, and taking the mean shot in each. 

 Mr. Kummell inquires what this discussion will lead to. It is cer- 

 tainly too rough for a limited number of shots, and whatever curves 

 may be found in any special case, they will be sufficiently near 

 ellipses, 'as required by Poisson's assumption. 



The Drift North of Lake Ontario. 



The short paper upon this subject read by Prof. J. W. Spencer 

 before the Philosophical Society at its last meeting was a general- 

 ized description of some of the obscure and conflicting phenomena 

 of the drift. 



Among the deposits of the later pleistocene period, he said in 

 substance, there is a well stratified, hardened, brown clay charged 

 with pebbles more or less glaciated, resting upon typical blue bowl- 

 der clay, north of Toronto. In the Canadian classification of the 

 pleistocene deposits there is no place for this deposit. Indeed, all 

 of the stratified deposits of this region need revision in the light of 

 the progress that has been made in surface geology during the last 

 twenty years. Thus the Saugeen clay is resolvable into three series. 

 The relation of all the clays to the older beaches requires special 

 study, as a part of them probably represent the deep-water deposit 

 of the beach epoch, while some of the later beaches rest upon such 

 clays. 



Around the head of Georgian Bay there are ridges in the form of 

 moraines, similar to those about the other Great Lakes, reaching to 

 the height of thirteen hundred to fourteen hundred feet above the 

 sea. From the face of the Niagara escarpment — between Georgian 

 Bay and Lake Ontario — there extends for over a hundred miles, to- 

 near Belleville, a broad zone of from eight to twenty miles in width,^ 

 covered with drift-ridges composed of stony clay below, and fre- 

 quently stratified clay or sand above, having an elevation of from 

 eleven hundred to twelve hundred feet above the sea, with occasion- 

 al reductions to nine hundred feet. These ' Oak Hills or Ridges ' 

 rise from three hundred to five hundred feet above the flat paleozoic 



