BIGELOW: EARLY DEVELOPMENT OF LEPAS. 65 



for me the eggs of Lepas hillii, Pollicipes polymerus and Sacculina, which 

 have been used for comparative study. 



In Vineyard Sound and Buzzard's Bay, groups of Lepas fascicularis, 

 L. anatifera and L. pectinata have been found at various times between 

 June and September. Any of these forms may appear at times when 

 the prolonged south-east winds have carried the drifting material of the 

 Gulf Stream in the direction of the Elizabeth Islands. So many elements 

 of chance are involved in getting the animals that it has been found 

 difficult to collect complete developmental series, and the work has been 

 often delayed. 



A very large majority of the animals of all species carry eggs in ad- 

 vanced stages of development when they arrive in the waters near Wood's 

 Hole. This has been found especially true of the numerous specimens 

 of L. fascicularis, hundreds of which have been found carrying eggs ready 

 to hatch, but only a few dozen with eggs in early cleavage stages. In 

 two different summers a few animals of this species have been found 

 early in June with eggs in stages of maturation, but when large numbers 

 of animals arrived in July, few cleavage stages could be found and in 

 many cases Nauplii were escaping from the brood-lamellae. 



Much drifting timber carrying L. anatifera was obtained about the 

 middle of August, 1898. The adult animals all carried eggs which were 

 in advanced stages of development and were hatching rapidly. Many 

 animals which were about half the adult size were laying eggs. The 

 timbers were anchored in the harbor, and for several weeks it was possible 

 to obtain an abundance of material in maturation and cleavage stages. 

 The stages of living and preserved material thus secured for study rep- 

 resented the important phases of every mitotic division in the early 

 development. 



As is well known, the development from egg to Nauplius takes place 

 in the mantle chamber. The eggs, each enclosed in a vitelline membrane, 

 lie in the cavities of the egg-plates, or ovigerous lamellae, which lie be- 

 tween the body and the mantle. In studying living ova it is easy to tear 

 the lamellae and thus free large numbers of eggs, but in preserving mate- 

 rial it is more convenient to fix the lamellae in large pieces. 



Maturation and cleavage were studied first in the living eggs. It was 

 found impossible to keep eggs developing normally under artificial con- 

 ditions outside the mantle cavity longer than from five to ten hours. 

 Other workers on Cirripedia have had the same experience. It was 

 rarely possible to follow a single egg through the maturation phases to 

 the close of the second cleavage, and fresh material, which had under- 



