i3 9 6. CORRESPONDENCE. 287 



coming memoir I shall further show that in the later development the appendages 

 become more and more complex in the successive stages. Professor Chun has 

 apparently omitted to take into consideration the possibility of change at successive 

 stages, and nowhere mentions the circumstances that the larvae compared were of 

 different ages. As a matter of fact, the differences between his observations and my 

 own nearly completely disappear when the corresponding sixth stages are compared, 

 but not quite, for actual differences do exist in the different species at this stage. I 

 see no reason to depart from the view I maintained, that there is an almost perfect 

 agreement between the different species during the first two stages. 



With reference to Dr. Giesbrecht's remarks, which I saw soon after the publica- 

 tion of his beautiful monograph, it seemed to me unnecessary to reply to them, as I 

 thought it would be perfectly apparent to anybody reading the communication by 

 Dr. Loeb and myself that the above-mentioned observer had not read the paper, at 

 any rate with the care that adverse criticism ought to presuppose, for his remarks 

 show a complete misapprehension of our statements. 



In the first place, with regard to the statement that the part of a cylindrical 

 vessel filled with water is brightest on the side remote from the source of light, I 

 may say that we took some pains to make it clear that it was not necessarily towards 

 or away from the most brightly-iliuminated spots that the Nauplii moved, but in the 

 direction of the rays of light, and that a Nauplius in the positively heliotropic condition 

 {i.e., moving towards the source of light) might be made to pass from a more 

 brightly to a less brightly-illuminated region, and vice versa. 



In the second place, the rays of light did not always pass through the convex 

 glass front of the vessel, but in many experiments obliquely from above through the 

 water only. 



Thirdly, the vessels used were by no means always cylindrical ; receptacles of 

 all shapes were employed, including long cylindrical glass troughs with upright 

 sides. 



I may lastly add that a later experimenter (Viguier), while severely criticising 

 our views, confirms our observations as to the existence of positive and negative 

 conditions of heliotropism in Cirripede Nauplii. Theodore Groom. 



Royal Agricultural College, Cirencester. 

 February 10, 1896. 



[Though it is not our business to take up the cudgels]for Mr. Groom's opponents, 

 still we suggest that it is inaccurate to say that Professor Chun "nowhere mentions 

 the circumstance that the larvae compared were of different ages," for, having stated 

 on p. 81 that the Nauplii under his observation had "obviously undergone the last 

 moult before passing into the Cypris-stage," on p. 87 he says, "the first antennae 

 (antennula) always, as is well known, uniramous, I find in agreement with the state- 

 ments of Dohrn (1870, p. 603), and Willemoes Suhm (1S75, p. 143), in all observed 

 Nauplii composed of six joints. Buchholz (1869, p. 30) and Groom (1894, P- I 79) 

 give the number of their joints in the younger Nauplii of the Lepads and Balam as 

 only four, while Lang (1876, p. 109), found them in the Balanid-Nauplii five-jointed." 

 To the second antennas Chun assigns an eight-jointed exopod and a four-jointed 

 endopod, nine and three being the corresponding numbers given by Groom, while to 

 the mandibular feet Chun assigns a four-jointed exopod and three-jointed endopod, 

 in contrast with the numbers five and two given by Groom. 



It was surely impolitic on Mr. Groom's part to ignore a criticism appearing in 

 such a work as the " PelagischeCopepoden." If we rightly understand the explana- 

 tion now offered, it is in the nature of a plea of " confession and avoidance," not 

 rebutting Dr. Giesbrecht's accusation, but claiming that, under the circumstances, 

 the error imputed was of no consequence. — Ed. Nat. Sci.] 



Geological Maps. 



The colour-printing of Geological Survey Maps alluded to in your February 

 number (p. 142) is certainly a welcome departure ; for, on account of the price, the 

 amateur, as distinct from the professional, geologist has hitherto had to colour his 

 own maps from such copies as he could beg or borrow. 



