422 Mr. H. J. Carter on the Eejjroduction of Sponges. 



same species. Neither of us lias ever seen two different spe- 

 cies of Dijflugice in zygosis, which is not less significant of 

 the act being for sexual reproduction than that the individuals 

 engaged in it are not mere varieties of one species, as some 

 would have it. 



I have also long since tried to find out the whole bearing of 

 this phenomenon in connexion with the oviform bodies found in 

 both the Difflugice and Amoebcv, and from time to time have 

 recorded what I have observed, by illustration as well as de- 

 scription, which those who wish to consult my contributions 

 in this respect may find in different numbers of the ' Annals,' 

 viz. in vol. xviii. p. 115 (1856^, vol. xii. pp. 30 & 2G1 (1863), 

 vol. xiii. p. 23 (1864), and vol.' xv. p. 171 (1865), since which 

 time I have not returned to the subject. I had hoped to 

 publish a figure, now in my journal, of zygosis in D. urceo- 

 lata-i in which every detail was measured and drawn upon 

 the same scale, that the relative sizes of all might at once 

 be seen ,• but, thinking that this might be indefinitely post- 

 poned, on account of my studies having taken another direc- 

 tion, I published the description of it in my last paper on the 

 conjugation of certain species of Diatomacea?, viz. that in the 

 ' Annals,' vol. xv. above mentioned. 



Finding that I could obtain no more knowledge of the pro- 

 cess by mere observation of it externally, I tried what the 

 effect of crushing and tearing to pieces a pair of D. urceolata 

 (for this is the largest and thus best adapted species that I 

 have found for the purpose) under the microscope, with the 

 following results, which, as a kind of ultimatum on the sub- 

 ject, was thus published in the paper last mentioned : — 



" Returning, then, to the question of impregnative genera- 

 tion in the Diatomeaj, it seems to me that, being so closely 

 allied to the Rhizopoda in their organization, they might be 

 inferred, by analogy, to follow the same mode of producing an 

 impregnated generation as Diffiugia. That this mode has 

 been demonstrated, I by no means wish to assert ; but obser- 

 vations on the subject, made subsequently to those published 

 in my last communications to the ' Annals,' still further sup- 

 port me in the views therein announced, viz. that the nucleus 

 furnishes the sjyerm-, and some other part of the body of the 

 Dijfjlugia the germ-cells^ which produce the new generation. 

 For in that large species which I have designated urceolata in 

 my last communication, and which I have since ascertained 

 to be one of the most persistent and plentiful forms about this 

 neighbourhood, I, last summer, almost invariably found the 

 nucleus (instead of undergoing the change as a whole) to be- 

 come divided into several spherical cells of equal size, each of 



