158 BULLETIN OF THE UNITED STATES FISH COMMISSION. 

 THE DEVELOPMENT OF THE SEMINAL RECEPTACLE. 



Development of the seminal receptacle is illustrated by figs. 79, 81, 89, and 98 ; 

 plates 32 and 33. Fig. 98 is drawn from the molted skin of the fifth larva. The sex 

 is not determinable with certainty, but it is highly probable that this is from a male; 

 the sterna of the sixth to eighth thoracic segments (marked 3-5 in figure) are clearly 

 defined. The sternal processes of the seventh thoracic segment are fused on the 

 middle line, where they are distinctly depressed. The unpaired middle piece is 

 marked as a slight transverse ridge or forwardly directed fold. It is clearly seen 

 in the sternum of the adult male, where it is not so distinctly wedge-shaped or so 

 intimately united with the wing like sterna of the preceding segment. Three suc- 

 cessive stages in the development of the seminal receptacle are shown in figs. 89, 79, 

 and 81, plate 32; they are from young lobsters measuring 21.2 mm. (eighth stage, 

 No. 3, table 34), 35 mm., and 52 mm., respectively. If these are compared with the 

 condition in an adult lobster (fig. 130) we observe the following external changes: 

 The sterna of the seventh segment, which are united on the middle line, diverge from 

 their anterior extremities, forming a wide angle. The sternum of the eighth thoracic 

 segment consists of a tongue-shaped fold (fig. 81) and a pair of backwardly diverging 

 rods. The former is constricted off as a single piece, though originally paired, and 

 develops into the wedge-shaped process seen in the adult organ. It grows forward 

 into the narrowing angle made by the wing-like process of the preceding sterna. A 

 secondary cleavage or division of the united sternal pieces of the seventh thoracic 

 segment is now going on, and the cleft thus formed is the permanent opening of the 

 seminal chamber. The latter is formed by the approaching walls of the wing-like 

 folds of the seventh thoracic sternum and tongue-like process derived from the eighth 

 thoracic sternum. 



THE MALE REPRODUCTIVE ORGANS. 



TESTIS. 



Each testis of the lobster is a grayish white sacculated tube consisting of anterior 

 and posterior lobes. There is no union between the organs of opposite sides. The 

 testis of the lobster was figured and described by Milne Edwards, and its structure 

 has been studied by Grobben (83) and Sabatier (173). According to Grobben, it is 

 made up of (a) a capsular membrane, (b) tunica propria, and (c) the spermatogenous 

 epithelium. Underneath the tunica propria a delicate, structureless membrane was 

 seen. The epithelium is differentiated into spermatoblasts, from which spermatozoa 

 are developed, and a syncytium — the ErsatzTceim — from which new spermatoblasts are 

 derived. The spermatoblast is regarded as homologous with the egg cell, the Ersatz- 

 keim with the follicular epithelium. A reserve albuminous material is laid down in the 

 spermatoblast for use in the development of the sperm cell. 



VAS DEFERENS. 



The vas deferens or seminal duct is shown as it appears in its natural position on 

 one side of fig. 120 and when dissected out on the other side. It consists of three fairly 

 distinct sections: (a) A proximal segment (Zuleitungs-Abschnitt of Grobben), which 

 serves to conduct the sperm from the testis ; a very slender tube of uniform caliber, which 

 curls, often in an irregular manner, over the posterior lobe of the gastric gland. This 

 passes very abruptly into the enlarged (b) glandular segment, where the tube bends 

 backward upon itself. It then turns forward again and, in somewhat the form of the 



