March 4, 1880] 



NATURE 



4i5 



neither forked nor branched when they fall into one of 

 the three families— Codonida?, Tiarida:, or Margelida?. 

 If the tentacles are branched or forked they belong to the 

 family Cladonemida?. These medusa: all are borne as 

 buds upon hjdroid polyps of Allman's sub-class Gymno- 

 blastea, sometimes called the Tubularina?. Fifty genera 

 of Anthomedusa? with one hundred and twenty species 

 arc described, and many are beautifully figured in the 

 plates of Haeckel's work. 



The LEPTOMEDUSJE are characterised in addition to 

 the points above noted by very often possessing marginal 

 otocysts or auditory vesicles. Those which have none 

 have eye-spots instead and belong to the families Thau- 

 mantiada: and Cannotida:; whilst those with otocysts 

 usually have no eye-spots, often have more than one 

 hundred tentacles, and belong to the families Eucopida? 

 and .Equorida:. Whenever the life-history of the Lepto- 

 medusa 1 has been traced tbey have been found to be 

 budded off from those hydriform colonies known as the 

 Calyptoblastca: or Campanularina? ; but many have never 

 been traced (/Equorida:) and perhaps develop direct from 

 the egg. Sixty-one genera and one hundred and forty 

 species of Leptomedusa: are described by Haeckcl. 



Of the two Trachyline orders the Trachomedus.e, with 

 canal-genitals, vary according as the stomach is elongated, 

 tubular, and devoid of a solid stalk (Petasidae and Trachy- 

 nemidae), or short, bell-shaped, and placed on the end of 

 a freely hanging solid stalk (Aglaurida? and Geryonidas). 

 Thirty-six genera and sixty species of Trachomedusae are 

 described and many new ones figured. It is to the genus 

 Carmarina of this group and Cunina of the next that 

 Haeckcl seventeen years ago devoted most careful study, 

 making known then in a most admirable monograph 

 (Jenaische Zeitschri/t, vols. i. and ii.) the excessively 

 elaborate structure of these forms, far exceeding in 

 histological differentiation and complex adaptation of 

 structure to function anything known in the other 

 Hydromedusa?. Here long since Haeckel had described 

 a highly complex nervous system and sense-organs which 

 recent investigations have confirmed and extended to 

 other groups. 



All the details of this work are fully summarised in the 

 most systematic way in the present volume. Under the 

 heading " Order— Trachomedusae " we have, as in the 

 case of each previous order, a systematic survey of the 

 various organs, their histology, and external form ; again, 

 under each family a similar survey, narrower in scope 

 and minuter in detail is given and finally each genus 

 and species in turn has its special features not already 

 included in what has been said of the family, fully 

 exposed. 



The second order of Trachylina?, the Narcomedusa?, 

 with gastral-genitalia, have, in addition to the characters 

 noted in the paragraph above, their auditory tentaculo- 

 cysts provided with otoporpae or rivets, which fix them 

 into the jelly-like substance of the umbrella, and which 

 are similar in origin and character to the curious peronia: 

 by which the tentacle-roots plunged as it were into the 

 sides of the umbrella-jelly (not therefore placed at its 

 margin) are connected with the hard marginal ring of the 

 umbrella. The Cunanthidas and Peganthidae are the 

 families which possess otoporpae, whilst the /Eginidae 

 and Solmaridae, though possessing peroniae, have no 



otoporpa?. Twenty-three genera and seventy-five species 

 of Narcomedusa: are described, and several figured. 



We thus have no less than four hundred species of 

 Hydromedusa: described by Trof. Haeckel, but he is 

 careful to point out with reiterated emphasis in reference 

 to each order, that since the Medusa: described are 

 known in the course of their individual growth and 

 development to alter their characters very much— such as 

 number and position of tentacles, of radiating canals, and 

 of sense-organs— and since at the same time it is known 

 (just as in the vertebrate Amblystoma) that these Medusae 

 may and often do become sexually ripe before they have 

 completed their changes, in fact whilst they arc still very 

 far from full growth or elaboration (pa:dogenesis) — it is 

 not obvious what we are to consider a " bona species" 

 among medusae. What, again and again, asks Haeckel, 

 is the criterion of a good species among Anthomedusa?, 

 among Leptomedusa?, among Narcomedusa?, among 

 Trachomedusa: ? The inference is that there is no 

 criterion, there are no such things as "good species." 

 We must be content with form-species ; which, in fact, is 

 all that we, as a rule, can get at or know anything about, 

 even in other animal groups. 



It need hardly be said that this splendid book is one 

 which every zoologist must study and enjoy. 



E. Ray Lankester 



LIGHTNING CONDUCTORS 

 Lightning-Conductors ; their History, Nature, and Mode 

 of Application. By Richard Anderson, F.C.S., F.G.S., 

 M.Soc.T.E. (London : E. and F. N. Spon, 1879). 

 TV/I R- ANDERSON deserves the thanks not only of 

 ■1- ' -*■ the scientific world but of the public at large for 

 the very excellent and readable volume which he has 

 produced upon the subject of lightning-conductors. 

 There are few persons who can lay claim to the amount 

 of practical experience which Mr. Anderson brings to 

 bear upon the subject, and still fewer who add to practical 

 experience an extensive and accurate knowledge of all 

 that has been done and written upon the subject on the 

 Continent, in America, and in this country. 



The earlier chapters of the author's work are almost 

 purely historical ; and, beginning with the days when 

 von Guericke first produced sparks and flashes from his 

 rude globe of sulphur, and when Hauksbee and Gray 

 speculated on the analogies between the crackling sparks 

 and the grander phenomena of thunder and lightning, 

 the reader is made acquainted with the various stages of 

 experimental discovery down to the time of Franklin. 

 From Franklin's letters the author quotes the following 

 memorable and characteristic extract, giving in his own 

 words the reasons which suggested to him the experiment 

 which rendered him famous : — 



"Electrical fluid agrees with lightning in these par- 

 ticulars : — 



" 1. Giving light. 



" 2. The colour of the light. 



" 3. In the crooked direction of the flame. 



"4. In the swift motion. 



" 5. In being conducted by metals. 



"6. In the crack, or noise, of the explosion. 



" 7. The subsisting in water, or ice. 



"8. In the rending of bodies it passes through. 



" 9. In destroying animals. 



