the membrane forms an irregularly folded thickening by means of which the lamella is attached 

 to the wall of the sack and which therefore represents Darwin's "ovigerous frenum". 



The eggs are not spherical (as those of I. quadrivalvis, according to Darwin) but 

 oval, the proportion of the longest to the shortest diameter being in one case as 40 to 34, in 

 another as 40 to 30. The size of the eggs was found to be different in different specimens : 

 the larger females probably producing larger eggs. The eggs of a small female from Labuan 

 Badjo (West coast of Flores) measured 0,14X0,1 mm.; development was only beginning. A 

 larger female taken from the corals of the island of Billiton contained eggs of 0,21 X o, 16 mm.; 

 these eggs showed the larva nearly quite developed, with the black Nauplius-eye, the three 

 pairs of legs etc. 



(Darwin does not give the size of the eggs for /. Cumingi\ one of the specimens of 

 that species collected in Molo Strait was furnished with egg-lamellae. The eggs had the same 

 shape as those of /. sibogae. Their greatest and shortest diameters measured 0,18 and 0,13 mm.) 



The size of the specimens is as variable as their shape. The larger specimens from 

 the different Stations have a length from 17,5 — 10 mm. The longest specimens are rather 

 narrow : thus the specimen of 17,5 mm. in length is nowhere broader than 4 mm. and its breadth 

 measures 2,3 mm. where narrowest. The stoutest specimen of all had a length of about 14 mm., 

 its breadth being 6,5 to 7 mm. in the upper part and in the inferior part of the peduncle it 

 was nowhere narrower than 5 mm. 



A few of the specimens are attached to little pieces of stone, in one case two, in another 

 four being situated on different sides of one stone. A few were found attached to a piece of 

 broken shell of a Balanid. Most of them, however, are quite loose. The inferior extremity of 

 the peduncle forms a flat disc in numerous specimens, and it is with this disc that the animal 

 is cemented to the stones or other objects on the bottom of the sea. 



Males 



I opened a dozen specimens of the females of I. sibogae and found with a few exceptions 

 only one or two males attached to the wall of the sack. They were of very different size and 

 development: as a rule they were small and immature, in two cases I found them relatively 

 laro-e and undoubtedly full-grown. But even in the latter cases I found a considerable difference 

 in size between the two males attached to the same female. The figure 20 of PI. IV shows two 

 laro-er males as they were found in situ~\ whereas the larger has a length of about 3,5 mm., 

 the other measures only 2,5 mm. The other full-grown couple of specimens showed about the 

 same proportions and dimensions. 



The immature or not quite mature specimens varied in size from 1,1 to 1,4 mm., one of 

 them measuring only 1,8 mm. The latter showed the testes in nearly quite developed condition. 

 Males of 1,4 mm. were in several cases found attached to the sack of a female which was 

 provicled with ovigerous lamellae. 



The number of males attached to a female is as a rule two ; they are found attached 

 to different parts of the interior wall of the sack, but seldom at the place where Darwin found 

 the little male of /. Cumingi, viz. "in a nearly central line, at the rostral end". I found them 



51 



