512 



NATURE 



\April 12, 1877 



which conjugates, and which is furnished with only two 

 cilia. The only distinction between the macro- and 

 microzoospores seems t© be that the former have four 

 cilia, the latter only two. When the microzoospores fail 

 to conjugate they may develop non-sexually just like the 

 macrozoospores. This is a fact of the highest importance. 

 In this plant, belonging to the lowest group in which 

 sexual reproduction occurs, the sexual and non-sexual 

 zoospores are hardly to be distinguished, and if by any 

 chance union of the sexual zoospores does not take place, 

 the zoospore behaves like a macrozoospore and develops 

 non-sexually. 



After remaining in a state of rest, sometimes for nearly 

 twelve months, the contents of the zygospore break up 

 into zoospores, from which arise the filamentous stage 

 of Ulothrix. 



In Ulothrix the conjugating cells are generally mor- 

 phologically and physiologically identical, but sometimes 

 larger zoospores conjugate with smaller, a difference in 

 sex being here indicated. In other cases the micro- 

 zoospores which have not conjugated germinate and give 

 rise to individuals capable of reproducing. The study of 

 the formation and subsequent development of the 

 zygospore shows that the product of conjugation is to be 

 considered as a new sexually-produced generation. It is 

 a unicellular plantlet, with a root-like process and a 

 slowly-growing plant-body which performs the function 

 of assimilation. It in fact represents the embryo and the 

 sporophore of the Pteridophytes. The root-end of the 

 plantlet is formed by the union of the germinal spots of 

 the conjugating microzoospores, while the assimilating 

 plant-body represents the united chlorophyll-bearing parts 

 of the zoospore. 



The Ulothrix is thus one of the Zygosporeas, and is 

 probably related to Hydrodictyon, but it shows certain 

 affinities to Spha^roplea, the lowest of the Oosporese. 



As this part concludes the tenth volume of this serial, 

 a most useful table of contents and special index of 

 names of plants and details treated of in all the papers 

 in the ten volumes has been added by Herr Zopf. This 

 enables the student at once to refer to any given plant, or 

 even to the part of it described in the various papers. 



W. R. McNab 



THE ROYAL NAVAL COLLEGE, GREENWICH 



r\^ February I, 1873, the Royal Naval College was 

 ^^ opened at Greenwich, " for the purpose of providing 

 for the education of naval officers of all ranks above that 

 of midshipman in all branches of theoretical and scien- 

 tific study bearing upon their profession." The first 

 annual report on the Royal Naval College thus esta- 

 blished has been recently presented to both Houses of 

 Parliament. 



When the College was established it was determined 

 by the Admiralty to bring together in it all the necessary 

 means both for the higher education of naval officers and 

 also of others connected with the navy. During the 

 session which terminated last year four captains, four 

 cornmanders,' ninety-three lieutenants, and eight navi- 

 gating-lieutenants joined the college as students, but 

 of these only one captain, thirty-three lieutenants, and 

 three navigating-lieutenants went through the whole nine 

 months' course, although one captain, two commanders, 

 fifty lieutenants, and three navigating-lieutenants under- 

 went the final examination. Besides these officers, who 

 may all be regarded as being purely voluntary students, 

 there was also a large number of others studying at the 

 college, with a view to passing certain examinations, 

 which would qualify them either for promotion or ad- 

 vancement or for appointment to some special branch or 

 department of the service. 



Fmally, ten private students are reported as having 

 passed through a course of instruction, nine of the 



number being foreign officers, a fact which testifies to the 

 estimation in which the college is held abroad. 



With regard to the subjects of study we find that, be- 

 sides the course of mathematics, which is compulsory for 

 all students, systematic courses of instruction, extending 

 over the entire session, are given in physics, chemistry, 

 steam, navigation, and nautical astronomy, marine sur- 

 veying, permanent and field fortification, miUtary survey- 

 ing and drawing, military history, foreign languages — 

 namely, French, German, and Spanish — and in freehand 

 drawing. Special courses of lectures are also given on 

 various subjects, among which the principal seem to be 

 the Structural Arrangements of Men-of-War, Interna- 

 tional Law, Naval History, and Practical Ship-building. 



TYPICAL LA WS OF HEREDITY 1 

 II. 

 Tp^RST let me point out a fact which Quetelet and all 

 ■*• writers who have followed in his paths have unac- 

 countably overlooked, and which has an intimate bearing 

 on our work to-night. It is that, although characteristics of 

 plants and animals conform to the law, the reason of their 

 doing so is as yet totally unexplained. The essence of the 

 law is that differences should be wholly due to the collec- 

 tive actions of a host of independent -petty influences in 

 various combinations, as was represented by the teeth of 

 the harrow, among which the pellets tumbled in various 

 ways. Now the processes of heredity that limit the 

 number of the children of one class such as giants, 

 that diminish their resemblance to their fathers, and kill 

 many of them, are not petty influences, but very im- 

 portant ones. Any selective tendency is ruin to the law 

 of deviation, yet among the processes of heredity there is 

 the large influence of natural selection. The conclusion 

 is of the greatest importance to our problem. It is, that 

 the processes of heredity must work harmoniously with 

 the law of deviation, and be themselves in some sense 

 conformable to it. Each of the processes must show this 

 conformity separately, quite irrespectively of the rest. It 

 is not an admissible hypothesis that any two or more of 

 them, such as reversion and natural selection, should fol- 

 low laws so exactly inverse to one another that the one 

 should reform what the other had deformed, because cha- 

 racteristics, in which the relative importance of the various 

 processes is very different, are none the less capable of 

 conforming closely to the typical condition. 



When the idea first occurred to me, it became evident 

 that the problem might be solved by the aid of a very 

 moderate amount of experiment. The properties of the 

 law of deviation are not numerous and they are very 

 peculiar. All, therefore, that was needed from experi- 

 ment was suggestion. I did not want proof, because the 

 theoretical exigencies of the problem would afford that. 

 What I wanted was to be started in the right direction. 



I will now allude to my experiments. I cast about for 

 some time to find a population possessed of some measur- 

 able characteristic that conformed fairly well to the law, 

 and that was suitable for investigation. I determined to 

 take seeds and their weights, and after many preparatory 

 inquiries, fixed upon those of sweet-peas. They were 

 particularly well suited to my purposes ; they do not 

 cross-fertilise, which is a very exceptional conditfon ; they 

 are hardy, prolific, of a convenient size to handle, and 

 their weight does not alter when the air is damp or dry. 

 The little pea at the end of the pod, so characteristic of 

 ordinary peas, is absent in sweet peas. I weighed seeds 

 individually, by thousands, and treated them as a census 

 officer would treat a large population. Then I selected 

 with great pains several sets for planting. Each set con- 

 tained seven little packets, and in each packet were ten 

 seeds, precisely of the same weight. Number one of the 

 packets contained giant seeds, all as nearly as might be 

 of -+- 3° of deviation. Number seven contained very 



' Lecture delivered at the Royal Institution, Friday evening, February 

 9, by Francis Galto.i, F.R.S. Continued ixowx p. 4q5. 



