336 



DISCOVERY REPORTS 



oval cells with round or oval nuclei, collect in the spermatophore sac together with 

 a large part of the secretion from the preceding part of the duct. The epithelium of 

 the sac secretes a chitinous cuticle, which encloses this mass in the spermatophore sheath. 

 The spermatophore is flask-shaped and lies in the sac with its head towards the external 

 opening. When fully formed it passes from the sac into the ejaculatory duct ej, the 

 muscular part of the vas deferens immediately adjacent to the external genital aperture 

 ega (Fig. 7), where it remains until transferred to the female. The lateral pocket Ip 

 functions as a cement gland, and its secretion adheres to the neck of the spermatophore 

 and serves to fix it on to the ventral surface of the female. In mature males, one 

 spermatophore is to be found in each ejaculatory duct, and another one in each sperma- 

 tophore sac, ready to take the place of the first after transference has occurred. The first 

 two pleopods in the male are especially modified to effect transference. 



DEVELOPMENT OF THE COPULATORY ORGANS 



The endopods of the first pair of pleopods show secondary sexual modifications before 

 any differentiation of the second pair 

 has begun. 



The endopod is at first quite typical, 

 consisting of a large blade-like setigerous 

 lobe si and a smaller rod-like auxiliary 

 lobe al (or appendix interna), which 

 carries a number of small hooks or cin- 

 cinnuli (Fig. 9). After a time, a blunt 

 oval lobe p grows out below the auxiliary 

 lobe: this is the first appearance of the 

 chief copulatory organ, the petasma 

 (Fig. 10). 



The petasma /> soon becomes cleft into 

 two parts, the inner lobe il carrying two 

 spines, and the median lobe ml carrying 

 one spine (Fig. 11). Growth of these 

 two lobes continues, the two spines on 

 the inner lobe occupying terminal and 

 proximal positions respectively, while 

 the spine on the median lobe becomes 

 lateral by reason of the extension of 

 the tip of this lobe. 



A fold, the wing W, running parallel pig. 9. First pleopod, undifferentiated. 



to the margin of the setigerous lobe also auxiliary lobe; si, setigerous lobe, 



develops (Fig. 12) and which, as growth F'g- ^°- First pleopod. Development of the petasma. 



1 ^1 ^ .A X -50. a/, auxiliary lobe; /), petasma; s/, setigerous lobe. 



contmues and the petasma extends ^ •' ^ *^ > > 5 



further over the surface of the setigerous lobe, curves over the two processes of the 



30- 



al. 



