July 30, 1891] 



NATURE 



291 



it out on a somewhat larger scale, so as to make his 

 volume represent for the biology of to-day what the 

 classical " Comparative Physiology " of Dr. Carpenter did 

 for the biology of forty years ago. The defect just 

 alluded to — if it be a defect — is one which can very 

 well be remedied hereafter, since the author will un- 

 doubtedly have an opportunity of expanding his book in 

 every direction in a later edition. 



Nearly half the book is devoted to the consideration of 

 the phenomena of life as exhibited by unicellular organ- 

 isms—the Protozoa and Protophyta. There can hardly 

 be any doubt that this is by no means an undue propor- 

 tion, since it is unquestionable that in these simplest forms 

 the fundamental problems of biology present themselves 

 in the clearest light. We have well-illustrated chapters 

 on Amoeba, on Hsematococcus, on Heteromita, on 

 Euglena, on the Mycetozoa, and then a comparison of 

 the foregoing organisms with certain constituent parts of 

 the higher animals and plants, viz. cells. The minute 

 structure and division of cells and nuclei are fully treated 

 and well illustrated. Then follow separate chapters on 

 yeast, on bacteria, on biogenesis and abiogenesis, and 

 on the more complicated unicellular animals— the Ciliata, 

 from among which are chosen Paramcecium, Stylo- 

 nichia, Oxytricha, Opahna, Vorticella, and Zoothamnium. 

 A chapter on species and their origin, and the principles 

 of classification, comes next, the illustrative examples 

 being chosen from among the Protozoa already described. 

 The Foraminifera, Radiolaria, and the Diatomaceae are 

 then brought under consideration. In every chapter the 

 organism or group of organisms treated is made to serve 

 as the concrete basis of a gradually expanding and con- 

 nected narrative. Thus, in passing to the consideration 

 of such forms as Mucor, Vaucheria, and Caulerpa, the 

 author says : — 



" The five preceding lessons have shown us how com- 

 plex a cell may become, either by internal differentiation 

 of its protoplasm or by differentiation of its cell-wall. In 

 this and the following lessons we shall see how a con- 

 siderable degree of specialization may be attained by the 

 elongation of cells into filaments." 



A pause is now made, and a brief but thoroughly up- 

 to-date chapter is inserted on " the distinctive characters 

 of animals and plants." Prof. Parker thinks there is a 

 great deal to be said in favour of Haeckel's third organic 

 kingdom— the Protista. I do not agree with him in 

 thinking that it is probable that the earliest organisms 

 were " protists," and that from them animals and plants 

 were evolved along divergent lines of descent. 



If we approach this question, not with the attempt to 

 define plants and animals verbally, but with the object of 

 indicating probable lines of descent, the groups some- 

 times considered as doubtful, and therefore "protist," 

 take rank with great probability either in the animal or 

 the vegetable series. The Mycetozoa and the Volvo- 

 cineas fit quite naturally in the animal series ; they 

 would be isolated among the Protophyta, and, conversely, 

 the Bacteriaceas are inseparable from the Oscillatorise 

 and other filamentous green plants. 



Prof Parker next proceeds to deal with plants of in- 

 creasing complexity of structure and function— Penicil- 

 hum, Agaricus, Ulva, Laminaria, and Nitella ; and, as a 

 parallel to these in the animal series, we have two chap- 

 NO. I 135, VOL. 44] 



ters, with excellent woodcuts, on Hydra and on the 

 Hydroid polyps, their colony-building and their alterna- 

 tion of generations. The extremely important facts and 

 theories of spermatogenesis and oogenesis and of fer- 

 tilization are next set forth, briefly but clearly, and in 

 sufficient detail for the general purposes of the book. I n 

 connection with the early development of the fertilized 

 egg-cell of the Metazoon from its unicellular phase to the 

 condition of the diblastula, the question is considered as 

 to how we are to suppose that the passage took place 

 historically from Protozoa to Metazoa or Enterozoa. 

 It is pointed out that there is a break here in the series 

 of living animals known to us, whilst there is no corre- 

 sponding break in the series of plants : there we pass b y 

 insensible gradations from unicellular forms to linear 

 aggregates of cells, and from these to superficial and to 

 solid aggregates. 



The Magosphcera planula described by Haeckel in 

 1870 is cited as an animal tending to bridge over the 

 gap in the animal series, but a footnote informs the 

 reader that "unfortunately nobody has since seen this 

 organism." Prof Parker probably is aware that this 

 is also true of Haeckel's Protomyxa aurantiaca, which 

 he figures and describes in an earlier chapter. It cer- 

 tainly is to be regretted that neither of these interesting 

 organisms has been observed again since they were de 

 scribed by Haeckel. However, Volvox globator is always 

 with us, and Prof. Parker gives an excellent set of figures 

 and a description of it, and proceeds to show how a two- 

 cell-layered sac— the ancestral gastrula or diblastula — 

 might have been derived from such a colony. He also 

 shows how a primitive diploblastic form might have deve- 

 loped from a multi-nucleate Protozoon, such as Opalina 

 or Oxytricha. 



In the laboratory it is convenient to take the Earth- 

 worm as an example of that central type of structure 

 which is found under various modifications in all the 

 Coelomate animals. Prof. Parker, rightly separating 

 himself from the ties of laboratory work, prefers the 

 marine worm Polygordius for his illustration of this 

 grade of structure, choosing it partly on account of its 

 greater simplicity, partly on account of its extremely 

 interesting and well-studied developmental history. As 

 the author contends, a student who reads the two chapters 

 here devoted to the anatomy, physiology, and develop- 

 ment of Polygordius, will have an immense advantage 

 either in his subsequent study of the Earthworm, or in 

 reverting to his notes of a previous dissection of that 

 worthy beast. The principle of the comparative method 

 will be revealed to him, and he will learn to distinguish 

 things essential from things non-essential. 



Next, with a rush, having scaled the long ladder leading 

 to Polygordius, Prof Parker takes his reader in one 

 chapter of seventeen pages through the anatomy and 

 morphology of the starfish, the crayfish, the mussel, and 

 the dogfish. This seems and is rather rapid, but the 

 rapidity is intentional and justifiable. By the aid of this 

 book the student is intended only to gain a general view 

 of the structure of those animals as comparable to that 

 of Polygordius. For further details he must go on to the 

 special study of animal morphology, physiology, and 

 embryology ; or having studied these subjects more 

 or less, he may, by aid of Prof. Parker's clever sche- 



