234 PROF. HUXLEY ON THE AGAMIC REPRODUCTION 



instead of forming groups between the egg-germs, in the non-geodephagous Coleoptera 

 and Hemiptera. They have been figured in Lepidoptera by Herold, Meckel, Thompson, 

 and Stein, in Diptera by Stein and Leuckart, and in Coleoptera by Stein. 



Secondly. In September last I received the fourth Part of the fourth volume of Moles- 

 chott's ' Untersuchungen,' which contains a long and remarkable Essay by Leuckart, 

 " Zur Kenntniss des Generations-wechsels und der Parthenogenesis bei den Insekten." 

 The first article in the memoir is on the " Alternation of Generations in the Aphides." 

 The author describes at length, and figures, the female reproductive organs oi Aphis Fadi ; 

 and although the arrangement of these organs is somewhat different from what obtains in 

 my Vacuna, I am happy to say that his account of the ultimate structure of the ovaries 

 essentially coincides with mine. The view which Leuckart takes of the relation of the 

 ova and agamic germs (p. 346) is also in close agreement with my own. I lay the more 

 weight upon these coincidences because Prof. Leuckart's observations must have been 

 made at the same time with, and were of course wholly independent of, mine. 



Lastly, not having the works of either Kaltenbach or Koch at hand when my memoir 

 was read, I abstained fi'om attempting to give the specific names of my Aphides. I have no 

 doubt now that the Adviparous form is the A])his Telargonii of Kaltenbach, especially 

 as my fi-iend Mr. Dallas, who has paid particular attention to the Hemiptera, is of that 

 opinion. The oviparous female resembles so much in form and habit the Vacuna dryo- 

 phila of Schrank, that I have little doubt it is really that species, though, when carefully 

 examined, the antennae are found to have six unquestionable joints, and seven, if the 

 swollen base of the last division of the antenna is to be regarded, as I believe it should 

 be, as a distinct joint. The eyes also have a small and inconspicuous tubercle ; and the 

 promuscis is not nearly so long as either Kaltenbach or Koch states. — Nov. 16, 1858. 



DESCRIPTION OP THE PLATES. 



Tab. XXXVI. 



Aphis Pelargonii. 



The letters have the same signification throughout. The fractions indicate the measured size, 



in parts of an inch, of the objects. 



Fig. 1. The three anterior chambers of a pseudovarium : a. the apical chamber; b. the second; 



c. the third, a. Pseudovarian ligament; b, wall of the pseudovarium; c. its epithelium; 



d. periplast or homogeneous matrix of the apical chamber ; e. clear vesicle ; /. its endoplast, 

 the two corresponding with the germinal vesicle and spot of an ovum ; g. a pseudovum par- 

 tially detached, its periplast greatly enlarged ; e'. its vesicle, whose endoplast is invisible ; 

 h. blastoderm ; i. pseudovitellus. 



Fig. 2. Terminal chamber of a pseudovarium, with the second chamber beginning to be formed in 



