THE GENEEATIVE ORGANS. 6 



Some of the more important results of my observations on 

 the development of Peri pa tus capensis, e. g. the derivation 

 of the mouth and anus from the blastopore, the fate of the 

 grooves in the cerebral ganglia, have already, some time ago, 

 been published in my paper^ " On the Origin of Metameric 

 Segmentation," and a preliminary account of them has been 

 (May, 1885) communicated to the Royal Society. 



All the drawings for Plates 1 and 2, with the exception of figs. 

 23 — 27, have been made by Mr. E. Wilson, of the Cambridge 

 Scientific Instrument Company. They are very careful and 

 accurate representations of the specimens, and I cannot suffi- 

 ciently express my thanks to Mr. Wilson for the great trouble 

 he has taken with them. The segmentation stages were all 

 drawn in the laboratory as I removed them from the uterus, 

 and the drawings^ form a permanent and accurate record of the 

 various stages of the living segmenting ovum. 



The Generative Organs. 



At the outset I must give a short description of the general 

 arrangement of the generative organs. Their minute structure 

 I shall describe more fully when I come to their development. 



Male Organs. — The description given by MoseleyS and by 

 Balfour* is correct so far as the general arrangement is con- 

 cerned, but a slight rectification is necessary in the significance 

 to be attached to the various parts. The structures called testes 

 by these authors (Balfour, loc. cit., PI. XX, fig. 43, te.) are ap- 

 parently merely seminal vesicles, in which the spermatozoa de- 

 velop and gain maturity. The true testes are the so-called 

 prostates (Balfour, loc. cit., fig. 43, pr.), the lining cells of 

 which fall into the cavity of the tube, pass into the swollen 

 seminal vesicle, where they develop into spermatozoa. The 



' 'Quart. Jour. Mic. Sci.,' 1884. 



^ I regret to say that the lithographer has not done justice to the original 

 drawings. 



3 ' Phil. Trans./ vol. 164. 



4 • Quart. Journ. Mic. Sci.,' 1883. 



