352 bulletin: museum of comparative zoology. 



For experiments with digestion fluids I made use of only formalin 

 material, since no alcoholic material was available, and albumins fixed 

 with salts of the heavy metals, e. g., osmium, are proverbially resistant to 

 peptonic digestion. On such preparations treatment with the Kuskovv 

 mixture of pepsin and oxalic acid does not alter either class of nucleoli 

 in the least, although cytoplasm is largely dissolved. So far, then, as 

 tests for albumins in the nucleoli go, the results are negative ; but from 

 the necessity of employing fixed material, they are not very important. 



D. Fertilization. 



The material was in this case fixed with 40 per cent formaldehyde and 

 stained with Grenadier's borax carmine, a combination which has proved 

 very satisfactory owing to the transparency of the eggs. Without study- 

 ing the living egg, which I have not done, it is impossible to follow the 

 actual penetration of the spermatozoon; so, with the statement that in 

 Gonionemus this always appears to take place just before the formation 

 of the second polar spindle, I pass at once to the consideration of the 

 nuclear phenomena involved. The earliest stage after penetration which 

 I have been able to study is represented in Plate 7, Figure 139. The 

 egg is now surrounded by a thick, transparent, vitelline membrane (Fig. 

 139), to which supernumerary spermatozoa are often attached. This is 

 fortunate, since it allows of a comparison between the sperm nucleus 

 within the egg and the spermatozoa which have not succeeded in pene- 

 trating. The egg nucleus, now in the early metaphase of the second 

 maturation division, lies midway between the centre and one pole of the 

 egg, the spindle axis occupying a paratangential position. About equally 

 distant from the opposite pole of the egg the sperm nucleus is clearly 

 visible. It consists of two portions, a deeply staining, apparently homo- 

 geneous, triangular or conical portion, — the head, — which is still but 

 slightly larger than that of the spermatozoon before penetration, and of 

 an unstained, rather refractive middle piece, which, as has been shown, 

 is of archoplasmic nature. No trace of the tail is to be detected. The 

 sperm structure as a whole forms the centre of a series of astral ra- 

 diations, the sperm aster, such as Maas ('99) has described in the fer- 

 tilization of the sponge Sycandra. With the advance of the second 

 maturation division, the sperm nucleus penetrates further and further 

 into the egg, and at the same time commences to undergo the series of 

 changes which are to fit it for actual conjugation with the egg nucleus. 

 The middle piece soon disappears entirely ; but the radiations persist, 



