July 21, 1892] 



NATURE 



273 



well able to take this step is proved by the character of 

 their pectoral limbs, which, unlike the fins of fish, are 

 provided with a transverse joint in the middle — " an elbow 

 joint "; and this, while clearly helpful in walking, would not 

 be well fitted for swimming. No doubt the animal was 

 also a swimmer ; the dorsal fin shows so much, but it was 

 also a walker, travelling over hard, uneven ground ; in- 

 deed, to this habit is attributable the turning up of the 

 tail-fin (!), which formed the third point of support. A 



Fig. 4. 



Figs, s to 4.— Embryos of Trochosasingoriensis. Fig. 2 on the r.^th day. 

 Figs. 3 and 4 on th<! isth day ; Fig 4, the anterior end seen en face, st, 

 stomatodaeum ; kl, frontal lobes ; ol, upper and ul, lower lip ; at, antennae ; 

 IV, wall-like thickening of marginal groove ; g\a, chelicerae ; g.yx, pedipalp; 

 gfia, ist pair of limbs ; th\a-th;^, thoracic appendages (2nd to'4th pairs of 

 limbs) ; a\a-aia, abdominal appendages ; .r, a deep constriction ; en, rudi- 

 ment of endopodite (after Jaworowski). 



drawing, subscribed " original," representing Pterichthys 

 " as it might have moved," is so full of unconscious 

 humour that we are tempted to reproduce it. From such 

 amphibious primitive vertebrates the fish branched off in 

 one direction and descended to the sea— the swimming- 

 bladder represents the original lung ; in another direction 

 proceeded the Stegocephala, the ancestors of reptiles, 

 birds, and mammals. Primarily the Vertebrata are derived 

 from Annelids, but the claim put forward for the Placo- 



FlG. S-— Pterichthys, a 



;ht have moved. (Original.) 



derms is more in harmony with Patten's view, connecting 

 them with the Arachnoids ; for the grave difficulties which 

 beset this view, however, let Smith Woodward's trenchant 

 criticisms be considered. 



The main line of argument is followed into a number 

 of collateral branches, all elaborately discussed. There 

 is a powerful chapter on the strand fauna, in which are 

 arrayed the great host of marine animals, including fishes, 

 which temporarily leave the sea to breathe the air. This 



NO. 1 1 86. VOL. 46] 



is regarded as a fact of profound significance, indicating 

 a general tendency of the strand fauna to come on shore. 



Recent investigations by Zacharias, Nusbaum, Chun, 

 and others are made good use of in discussing the distri- 

 bution of fresh-water fauna. Aerial transport, particularly 

 by birds, is accepted as accounting for most of the facts. 

 The survival of the transported forms is insured by the 

 chitinous investment either of the animals themselves or 

 more usually of their eggs. It is pointed out that most 

 pelagic fresh-water species are provided with means of 

 attachment : such are the spines of pelagic species of 

 Daphnia, the abdominal processes of Bythotrephus, and 

 the singular antennae of Bosmina. Copepods which lay 

 eggs which sink to the bottom are restricted in distribu- 

 tion ; those which carry them about in egg-sacs are 

 world-wide. 



An attempt is made to prove that fresh water opposes 

 some obstacle to the secretion of carbonate of lime ; and 

 though a comparison of the thickness of marine and 

 fresh-water shells is far from bearing this out, yet some 

 interesting results are elicited ; as, for instance, the 

 suggestion that the chitinous bristles of the young of 

 Paliidina vivipara are probably the last traces of ori- 

 ginally calcareous spines. 



In illustration of the various stages of land life, the 

 Testacillidas are cited as an interesting example of adap- 

 tation to a terricolous existence. Daiidebardia, one of the 

 family, begins life as a form precisely like a Hyalina, but 

 with growth passes through the successive stages shewn 

 in the figure (fig. 6) till it becomes the worm-like adult. 



A good deal of space is naturally devoted to the sub- 

 ject of encystment, which is regarded as a protection 

 against desiccation. In the course of this discussion an • 

 earlier origin is attributed to the Heliozoa than to the 



^^^f 



Fig. 6. — Daudebardia in different stages of growth ; on the right, youngest, - 

 on the left, oldest stages. The buccal mass is shaded. (Original.) 



Radiolaria, since they do not possess the central capsule 

 of the latter, which are consistently regarded as the 

 marine descendants of an ancient fresh-water group 

 related to Heliozoa. The suggestion is added that the 

 withdrawal of plasma in the Radiolaria into the central 

 capsule as a preliminary to spore formation is not really 

 with a view to this event, but a reminiscence of encyst- 

 ment, which occurred in ancestral fresh-water forms. 

 Bald suggestions such as this, and another which occurs 

 in the work, to the effect that chlorophyll first acquired its 

 fluorescence as the primaeval sky cleared of clouds and 

 permitted an extension of the solar light towards the 

 violet end of the spectrum, should, from motives of 

 prudence, have been omitted. A total bouleversement of 

 accepted views on main lines of descent is sufficient for a 

 great work without the added irritation of superfluous 

 conjectures. Summer and winter eggs belong more or 

 less to the question of encystment, and the author regards 

 winter eggs as " an adaptation to small pools, and 

 threatened destruction by drying up." This, like the 

 statement that the chitinous shells of the eggs of pelagic 

 Crustaceans were acquired as a protection against de- 

 siccation during their aerial flight, might have been ex- 

 pected from an ultra- Darwinian, but in an author who 

 wishes to explain evolution by physical causes, and not 

 by chance, it is less pardonable. "An adaptation to 

 threatened drying up" is an expression which would 

 please the metaphysicians, who have lately been con- 

 tending that an effect may precede its cause. 



The bibliography at the end of the work will be found 

 most useful, especially to Englishmen, who will find in it 

 a guide to a great deal of interesting German literature ; 

 but it is without form, and this to a great extent is true of 



