526 CRUSTACEA MALACOSTRACA. 



and (3) the capsule, corresponding to the region of the tail. 

 The last contains the two parts of the posterior centrosome 

 which lie in the " pars conjunctions " or basal region of the 

 tail of an ordinary spermatozoon. The capsule consists of 

 an outer "chitinous" envelope, an inner " chitinous " tube 

 investing the second division of the posterior centrosome, and of 

 a substance between (partly dotted in Fig. 322 a), capable of 

 swelling quickly in water. The swelling leads to sudden in- 

 version of the parts of the capsule, a result which is accom- 

 plished with " explosive " rapidity. 



Koltzoff finds that the spermatozoa, borne in a current of water, 

 on coming in contact with an egg adhere by the tip of one process, 

 then by a second, and finally by all three. By a shortening of the 

 processes the head is brought down to touch the egg membrane, 

 and then, propelled by the " explosion " of the capsule, the head 

 and the part of the neck containing the anterior centrosome are 

 made to penetrate the membrane. This is regarded as the 

 normal mode of fertilization. It should be stated however 

 that the subsequent nuclear changes have not been followed. 



Koltzoff divides the spermatozoa of Decapods into anacantha 

 which are without diverging processes and are found in the 

 Natantia, and acanthina, found in the other groups, and 

 provided with such processes. The latter are divided into 

 cephalacantha in which the processes spring from the region of 

 the head (Brachyura) and deracantha * in which they spring, 

 as in Galathea, from the neck. Finally the latter are again 

 divided into erecta, in which the several parts are arranged, as 

 in Galathea (Fig. 322 a), in a linear series, and contracta in which 

 the capsule, with an intervening layer representing the neck is 

 sunk into a depression of the head the whole having, as in the 

 case of the crayfish, the shape of a sphere with diverging 

 processes (Fig. 322 b and c).f 



The sexes are distinct in the Decapoda, though sexual dimor- 

 phism is less marked than in many groups of Crustacea. The 

 males are more abundantly supplied with olfactory hairs than 



* 5ep?7 the neck. 



f As spermatozoa acanthina, deracantha, erecta Koltzoff classifies those of 

 the Paguridae, Galatheidea and Homarus (the lobster), while the Loricata, 

 Thalassinidea and the crayfish (Astacus, Fig. 322 6) have according to 

 him spermatozoa acanthina, deracantha, contracta a difference between the 

 lobster and the crayfish which may raise a doubt as to the far-reaching 

 character of the distinction. 



