No. 1791. 



SPERM TRANSFER IN DECAPODS— ANDREWS. 



423 



two lateral lobes, one of which runs back under the anterior part of 

 each scale. 



A cross section between the fifth legs in one of the young females, 

 fig. 4, shows the scales as thick outgrowths of the shell arising from 

 the bod}^ at the sides and overarching a wide space, but not meeting 

 one another at the middle line. The young individual is thus inter- 

 mediate between the adults of P. setiferus and P. hrasiliensis in 

 having the scales much more extensive than in the former and much 

 less so than the latter. 



When the spermatophoral mass is present w^ithin the thelycum, 

 the internal relations of the organ are more complex and less easy 

 to understand, since parts of the sperm envelope may be mistaken for 

 parts of the thelycum. When the scales were dissected off from 

 museum specimens, the secreted mass that incloses the sperm was 

 seen as a large fiat bag-like mass stuck to the shelf as if a part of it. 

 The scales themselves were thick fleshy plates, fig. 4, hollowed out 



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Fig. 4.— Cross section of THELYCxm of a young Peneus beasiliensis, showing scales eight and left. 



on their dorsal faces to receive corresponding elevations of the 

 spermatophoral mass. The edges of the plates are flattened where 

 they join one another. 



The entire shelf is somewhat Y-shaped; each lateral part has a 

 deep groove to receive the downward bent anterior edge of the scale, 

 so that the space inclosed by the scales is very tightly shut off from 

 the external water. In the lengthwise section, fig. 5, this groove on 

 the scale {S) is seen with the edge of the scale {Sc) resting in it. 

 The space inclosed by the overarching shelf and the overgrown scales 

 is filled by the spermatophoral mass. This consists of a secretion 

 that breaks into thick lamellae in the preserved specimen and which 

 incloses the sperm, indicated by the dark central mass. 



The entire spermatophoral mass has a marked median keel between 

 the right and left scales and a large right and a left wing. The 

 inclosed sperm is chalky w^hite before staining and is completely 

 enveloped by the secreted mass, so that it would be well cut off from 

 tlie water as well as entirely concealed within the spermatheca or 



