476. KEPORT — 1895. 



occurs. Since sending in an account of my work to await publication, 

 two memoirs ' have appeared dealing with the same subject. The authors 

 have arrived at practically the same results, and as they all agree very 

 closely, it is unnecessary to recapitulate mine, at any length. It will be 

 sufficient to state that according to all three accounts there is nothing 

 resembling a 'quadrille'; the centrosomes and astrospheres owe their 

 origin to the ' body ' of the spermatozoon ; and there is no trace of an 

 egg-centi-e or egg astrosphere. In the tiner details, however, our accounts 

 differ somewhat, and I venture to think that Messrs. Wilson & Matthews 

 have entirely, and Professor Boveri partly, overlooked the true centro- 

 some. The two former authors describe the astrosphere as containing 

 no centrosome proper, but in its place a network closely resembling an 

 ordinary nuclear reticulum. This condition is maintained throughout. 

 Boveri, on the other hand, finds a minute deeply-staining centrosome 

 shortly after the sperm head has penetrated into the ovum. In the later 

 stages this centrosome swells up into a large hollow vesicle. I agree with 

 Boveri in his first statement, but believe that later on he has missed the 

 true centrosome, and has figured and described as a vesicle the ' heller 

 Hof,' for I find at this stage a deeply-staining sharply-defined centrosome 

 in the midst of a clear ' heller Hof.' My attention was chiefiy confined 

 to Sphaerechinus granularis, and it may be, though it seems highly 

 improbable, that a diflTerent process may take place in different species. 



In the tunicates PhaUusla viamiUata and Ciona intestinalis I found 

 much the same relations as in the Echinoderms as regards the origin and 

 behaviour of the centrosome, and for this investigation the Ascidian o\um 

 proved a very favourable object to study. I have been able to trace 

 carefully the maturation and fertilisation in rhallusia, and have coupled 

 my results in one paper with those T obtained from studying the 

 Echinoderms. I was also able, though with rathtr less certainty, to make 

 out the number and mode of division of the chromosomes during 

 maturation. The nucleus of the ovocyte I. (to use Boveri's well-known 

 nomenclature) contains eight chromosomes. From their subsequent 

 behaviour I see no reason to suppose that they form two ' Vierer Gruppen,' 

 but look upon them as of equal independent value. The eight chromo- 

 somes divide by transverse division into sixteen for each polar body, 

 eight therefore remaining in the nucleus of the ovum (female pro-nucleus). 

 There is therefore, here at any rate, no ' reducing ' or ' equalling ' division. 

 Owing to the very small size and close approximation together of the 

 chromosomes, this part of the work was attended with considerable 

 difficulty. 



The sperm head breaks up into eight chromosomes, and the first 

 segmentation spindle therefoie contains sixteen, the normal number for 

 the species. 



It would be out of place to discuss here the bearing these results may 

 have on points of general cytology, or on those theories of heredity which 

 have been based on observations of like phenomena in other forms, above 

 all, in Ascaris 7negaIocephala. 



Before closing this report, however, I should like to emphasise once 

 more the great advantages which an occupation of a Table at the Naples 



' Boveri, 'Ueber das Verhalten der Centrosomen bei der Befruclitungcles .Seeigel- 

 Eies,' Verhaiidl. des Phys.-mcd. (resell, zu IW'irzhurff, Bd. xxix., 1895. ]['ihoi! and 

 Mattlwrvs, ' Maturation, Fertilization, and Polarity in the Echinoderm Egg.' Journ. 

 of Morphol., vol. x., No. 1. 



