4. The complemeutal males. 29 



The pronuclei are often markedly lobed and this lobation may lead, as in the instance 

 figured on Plate 3 fig. 16, to the apparent presence of three pronuclei in the egg. So far 

 there has been no trace of an aster in the egg, but now this appears between the nuclei, as 

 shown in Plate 3 fig. 1 7, but its exact mode of origin is uncertain. Probably it emerges from 

 the male pronucleus. The aster divides and forms an amphiaster round the two pronuclei 

 whose membranes have begun to fade and in certain instances to coalesce (fig. 18). 



In the next stage (fig. 19) we see the fully constituted first segmentation spindle at the 

 periphery of the egg with the chromosomes arranged in the equatorial plate. The second 

 polar body (pb2) is clearly distinguishable beneath the egg membrane. 



Sections through the first segmentation spindle (metaphase figs. 20 and 20 a, telophase 

 21 and 21a give the chromatic number 24 — 28. i. e. twice the number which appeared in the 

 maturation phases. 



An interesting feature in the telophase of the first segmentation division (fig. 22) is that 

 the daughter nuclei are reconstituted at first not as single nuclei but as a number of smaller 

 bodies, each body containing a chromosome, which subsequently fuse to form the single nucleus 

 of either hemisphere. 



Such are the detailed processes of maturation and self-fertilization which occur in all 

 the batches of eggs, whether first or subsequent, in Peltogaster curvatus; and essentially the 

 same processes have been found to occur in Sacculina neglecta and Parthenopea subterranea, and 

 I do not doubt that they also occur in Lernaeodiscus, Triangulus, Heterosaccus and Clistosaccus. 



4. The coniplemental males. 



Plate 6 figs. 1 1 — ].">. 



A. Ill Sacculina and Peltogaster. 



We have shown so far that self-fertilization is the invariable rule in those Rhizocephala 

 hitherto considered: what then is the function of the so-called coniplemental males in these 

 animals V Lilljeborg (4) was the first to observe, but Fritz Muller (5) was the first to make 

 serious comments on this subject, and he found in young specimens of Peltogaster socialis that 

 there might be present a varying number of Cypris larvae fixed round the mantle-opening. 

 When he observed these larvae they were always dead and consisted of the mere chitinous 

 cuticle, but he judged from their position and from the analogy of other Cirripedes that they 

 were coniplemental males. 



Delage (9) extended these observations to Sacculina carcini, but never saw the larvae 

 alive. My observations have been made on Sacculina neglecta and are as follows. 



In about ninety per cent of the youngest Sacculinae externae, measuring from 1 — 3 mm 

 in breadth, a number of Cypris larvae varying from 1 — 19, have been found fixed round the 



