lvi 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 Anceidz 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 between the 
male and female Anceus. There is no doubt that the outward aspect of some of 
the little Pranizz, 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 afemale. [examined 
immediately the sexual parts of the specimen, and found a well-developed penis on 
the last exceedingly small segment of the pereion. There can be no doubt, therefore, 
that Praniza changes into Anceus.* 
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 says, that only the Anceus state is the adult state, and that, ‘‘quelques 
jours avant Ja transformation des Pranizes fémelles en Ancées les ceufs qui préexistent 
s’apergoivent 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 
devolopment in animals which are far from the Anceus period, which Mr. Hesse calls 
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 embryology 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 
antennz, one pair of mandibles, two pairs of maxille, 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 my 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 Praniza) which wre transformed into the Anceus 
state ; the females retaining their preceding form of Praniza. I 
