200 A. S. PACKARD, JR., ON THE 



acter of these gill-like divisions of the feet vary so as to be only a family or generic 

 character), while the frontal doublure and hypostoma of the Trilobites are directly homolo- 

 gous with those of Apus, I judge that the two groups belong here if anywhere among 

 the Crustacea. As to the points of disagreement, Dr. Dohru remarks on p. 609, "Only one 

 error which might possibly cause confusion, must I here notice. Dr. Packard considers 

 what I have above described as the exochorion, to be the true chorion ; and what I regard 

 as the chorion, he calls at one time inner egg-membrane, then amnion, and finally the 

 homologue of the 'larval skin' of German embryologists." 



I may say that at first I was, with Dr. Dohrn, disposed to regard the structureless cho- 

 rion as an exochorion, but after careful and repeated observations on the ovarian eggs, and 

 those that had begun to develop, I found that the egg was surrounded at the time of ovi- 

 position by but a single membrane, viz., the chorion; and that it was formed in the ovary in 

 the normal manner by being evidently secreted by the epithelial cells of the ovarian tubes, 

 as I could see them partially surrounding the partly formed eggs. After the examination 

 of hundreds of eggs freshly laid I failed to find any other membrane until just at the time 

 of the formation of the primitive disc. The observations and drawings I have presented 

 in this article, prove, I think, that Dr. Dohrn's "chorion" is the first blastodermic moult; as 

 I have observed, unless greatly mistaken, the membrane splitting off from the primitive 

 band. How successful I have been in homologizing this blastodermic moult with the 

 "amnion insectorum," i. e., of the hexapoda and the scorpions, I leave to the judgment of 

 embryologists. I might add that Gegenbaur (1. c.,p. 249) notices the transformation of the 

 cuticula into the egg membrane, but does not desciibe any other membrane in the egg. 



Secondly, Dr. Dohrn errs in saying that I have homologized this amnion with the 

 "larval skin." Indeed I have not mentioned them even on the same page (see American 

 Naturalist, iv, October, 1870, pp. 500, 501, and Proceedings of the American Association 

 for the Advancement of Science, published in August, 1871). What I then wrongly called 

 a nauplius skin, doubtfully referring it to the "larval skin" of German embryologists, I call 

 in this final article subzoeal skin, and the homologue of Van Beneden's "cyclopian skin." 



On p. 582, Dr. Dohrn states that in the earliest stage he could observe, there were 

 visible the rudiments of only five pairs of appendages. I might say that I have examined 

 hundreds (I believe over a thousand) living eggs, as well as those that had been hardened 

 in spirits, in order to ascertain whether the germ fii'st appears with less than six pairs of 

 legs, but without success. 



Dr. Dohrn does not regard the earliest condition of the embryo of Limulus as a nauplius. 

 I may say that in regarding the earliest stage of Limulus as a nauplius, which I have 

 done with some reservation, I was led to do so partly on theoretical grounds, on the principles 

 advanced by Dr. Dohrn himself in his able works on the embryology of Crustacea. If the 

 earliest stage of Daphnia (see his Untersuchungen fiber Ban und Entwicklung der Anthro- 

 poden, p. 56, pi. i, fig. 8), or Scyllarus and Palinurus (Zur Entwicklungs-geschichte der 

 Panzerkrebse, pi. xvi, figs. 3, 4) represented truly the nauplius stage, then it occurred to 

 me that the corresponding embryonic stage of Limulus represented a nauplius condition. 

 The greater number of limbs in the germ of Limulus seemed to me of slight consequence. 

 In either case the comparison with the nauplius of the Copepoda, or even of PeuiBus, is in 

 a degree hypothetical ; and many zoologists will probably regard the likeness as of little 

 significance unless strongly biassed by evolutional views ; just as the comparison of the 



