134 J. DUESBEKG 



and surround usually for a short distance the proximal part of 

 the tail. The shape of this sheath varies with the different spe- 

 cies. In Amphioxus the chondriosomes are represented by a 

 rather voluminous body in which, by careful study, one can 

 make out three to five granules. In Amia, such a body appears 

 indistinctly granular and fits the posterior part of the head as the 

 cup fits the acorn. In teleosts similar dispositions are found, for 

 the details of which I refer to Retzius' papers. I wish to empha- 

 size that in a number of species the granules are very distinct 

 and even constant in number. In Lophius piscatorius for in- 

 stance, Retzius ('10 b) invariably found four of them, disposed 

 in regular order around the origin of the tail. 



It may well be recalled that a similar disposition of the chon- 

 driosomes has been observed in invertebrates. For instance, ac- 

 cording to the observations of Meves ('00, '03), each spermatid 

 of the apyrene generation of Paludina vivipara contains four 

 chondriosomes. They assume the form of spheres and occupy 

 the posterior part of the head, where they surround the axile 

 filament. Bonnevie ('07) gives a similar description for Mem- 

 branipora pilosa. In these cases however, this stage is a tran- 

 sitory one, for the shape of the chondriosomes changes during 

 the further evolution of the spermatid, while in other inverte- 

 brates the same arrangement is, according to Retzius, retained in 

 the ripe spermatozoon, namely, i-n a number of celenterates ('04 a 

 and b; '05 a; '09 a), in many echinoderms ('04 a and b; '05 a; 

 '10 a), ^ in worms ('04 a and b; '05 a; '06 b, c and d; '09 b) and 

 in moMuscs ('04 a and b; '05 b; '06 a; '10 b). In many species 

 belonging to the two last-named classes the numerical constancy 

 of the chondriosomal spheres and the regularity of their arrange- 

 ment around the axile filament are conspicuous features of the 

 ripe spermatozoon. Especially remarkable is the disposition in 



1 Meves ('12) contests the accuracy of Retzius' description for Parechinus 

 miliaris. He finds that the so-called 'Mittelstiick' is not granular, as stated by 

 Retzius, but homogeneous, and that it has the shape of a ring, through which 

 runs the axile filament. I take this opportunity to remind how inadequate is the 

 expression 'Mittelstiick' or 'middlepiece,' as, between the 'Mittelstiick' of the 

 spermatozoon of an echinoderm, of a selachian or a urodele amphibian and of a 

 mammal, there is no homology whatever. 



