INTRODUCTION. 



must be, demonstrate, we think, the great amount of 

 interesting information that a more complete study of the 

 subject must elucidate. (C. S. B.) 



As the information conveyed in the following letter reached us too late to appear 

 in the Appendix, we think it but just to the author to publish it entire ; the 

 more so since, during the progress of his researches, we repeated them and know 

 their accuracy. 



MY DEAR SPENCE BATE, 



You are kind enough to ask me for a short abstract of my investiga- 

 tions in the anatomy of Anceidas which I tried to make when staying with _you 

 in Plymouth. I am the more glad to follow your request, since it is especially 

 your Memoir upon these animals that made me desirous to work on them. You 

 were quite right in directing the attention of observers to the internal structure 

 of these little Crustacea, for there are some points in their organization which were 

 not followed up by Mr. Hesse in his elaborate Memoir, and some points in which, 

 your opinion differing from that of the French naturalist, we had no certainty 

 about their real nature. 



I do not think that you are right in speaking of an early distinction bet ween the 

 male and female Anceus. There is no doubt that the outward aspect of some of 

 the little Praniza?, just having left the parent, makes more the impression that they 

 are to become Anceus, whilst others resemble more the female, or Praniza form. 

 But in giving special attention to that point, I found that this impression was 

 only due to the expansion of the segments of the pereion being greater or smaller 

 than to any real difference. Besides that, I kept some animals, which had rather the 

 aspect of females than males, during some time in a glass, and had the opportunity 

 of watching their moult. Two of them enabled me to see the large projecting 

 mandibles of the males within the head of what I thought was a female. I examined 

 immediately the sexual parts of ihe specimen, and found a well-developed penis on 

 the last exceedingly small segment of the pereion. There cj,n be no doubt, therefore, 

 that Praniza changes into Aiiceus.* 



This is what Mr. Hesse contended. But though I must agree with him in this, I 

 cannot but have another interpretation regarding the so-called larval or Praniza state. 

 Mr. Hesse fays, that only the Anceus state is the adult state, and that, "quelques 

 jours avant la transformation des Pranizes femelles en Ancees les ceufs qui prtiexistent 

 s'apercoivent a travers la peau." &c. In calling the eggs pre-existent, he is not, it 

 appears to me, justified, for they make their appearance very soon, and begin their 

 development in animals which are far from the Anceus period, which Mr. Hesse c~alls 

 their Anceus state. I agree, on the contrary, fully with you in calling the adult or 

 Anceus state one of a retrograde character, for every organ begins then to degene- 

 rate. 



Regarding the digestive apparatus, my investigations have led me to other results 

 than your remarks seem to show. I could observe the mouth and the whole intes- 

 tine in the old males as well as females. Those sacs, filled with green mass, are the 

 liver sacs, as the study of their embryolugy clearly states. The embryology clearly 

 indicates the Isopodous nature of the family ; but I must say that I never found, nor 

 expected to find, such forms as Mr. Hesse figures with a central red eye. There 

 certainly must be an error in his drawings. 



There is another puzzling circumstance regarding the conformation of the seg- 

 ments. In the adult there seems to be the want of one of the typical segments, and 

 you consider it to be either the first or second segment of the pereion. But my 

 embryological investigations show that all the typical segments are present, as in 

 other Isopoda. In the very early state of the embryo you will find two pairs of 

 antennae, one pair of mandibles, two pairs of maxillse, and seven pairs of feet. Every 

 one of these extremities corresponds with a segmental division of the body. But 

 there is between the last pair of the pereiopoda and the first pair of pleopoda a 

 segment whose extremities are wanting. This segment afterwards constitutes a 

 very small portion of the pereion, and is rather easy to be overlooked ; in the male 

 the penis is fastened to it. Counting that segment, you will find there is none 

 wanting in the composition of the body ; and you can be quite sure in calling the 

 first pair of the legs of the embryo the maxilliped, and the second the gnathopod, 

 for both are connected with the mouth in a very early state already. 



I could add some more particulars about the internal structure of the animal, but 

 it would hardly be of much use without adding plates to what I have to say. 

 What I have already stated will, however, show, that though there are some 

 anomalies about the Anceid;e, they are not of such extent as formerly was believed. 

 I hope, besides, to give a complete account of niy investigations in a short time in 

 one of our German periodicals. Yours &c., 



Messina, October, 1868. ANTON DOHRN. 



* It must not be forgotten, with reference to this too general expression, that it is 'only the male 

 individuals (having in the young state the form of Franizal which are transformed into the Anceus 

 state ; the females retaining their preceding f"vm of Praniza. I. O. W. 



