158 Mr. T. T. Groom. [June 16, 



XIV. " On the early Development of Cirripedia." By THEO. T. 

 GROOM, B.A., B.Sc., F.G.S., Demonstrator in Zoology at 

 the Yorkshire College, Leeds, late Scholar of St. John's 

 College, Cambridge. Communicated by ADAM SEDGWICK, 

 F.R.S. Received May 11, 1892. 

 (Abstract.) 



During a month's occupation of a table at the Marine Biological 

 Laboratory of Plymouth, in the summer of 1889, and a nine months' 

 occupation of the Cambridge University Table at the Zoological 

 Station of Naples, commencing in the October of the same year, I 

 had the opportunity of studying the development of a number of 

 Cirripedes. Since that time, investigations on the same group have ' 

 been carried on chiefly in the Morphological Laboratory at Cambridge. 



I have been wishful to take up this subject, because the embryo- 

 logy of Cirripedia had been considerably neglected since the intro- 

 duction of the more modern methods of investigation, and because the 

 development might reasonably be expected to throw light on the 

 adult structure of this interesting group. I wished, moreover, to 

 compare the development in several species, with the object of throw- 

 ing some light on larval evolution in general. 



The species studied were Lepas anati'fera, Linnaeus ; Lepas pectinata, 

 Spengler ; Conchoderma virgata, Speiigler ; Dichelaspis Darwinii, 

 Filippi ; Chthamalus stellatus, Poli, and Balanus perforatus, Bruguiere. 



Of Dichelaspis, only mounted specimens of the nauplii were 

 examined, but in the other forms the development from the freshly- 

 laid ovum to the second nauplius stage was investigated. 



I had expected to find notable differences in the development of 

 the different forms, but, although most of the genera could be dis- 

 tinguished at an early age, by some feature or other, the general 

 course of development was very uniform, and the following summary 

 is applicable to all the members of the group : 



The freshly-laid ovum consists of granular protoplasm, hollow 

 yolk granules, and oil globules. Its size has much more relation to 

 that of the nauplius than to that of the adult. 



First polar body is given off, not in the ovary, but in the mantle 

 cavity, though the first directive spindle is evidently formed in the 

 ovary. The polar body is formed independently of, and probably 

 before, or simultaneously with, fertilisation. 



Fertilisation takes place in the mantle cavity before the peri- 

 vitelline membrane is formed. 



The emission of the first polar body is immediately followed by the 

 formation of the vitelline (or peri-vitelline) membrane, which arises 



