1917 Fasten: on Decapoda 293 



deferens it is milky-white and viscid in consistency. However, in a short 

 while it changes to a firm blackish mass. This is in accord with the ob- 

 servations of Allen (1916), who describes reproduction in Panulirus inter- 

 ruptus in the following words: "Insemination takes place from a putty- 

 like mass of sperm material placed upon the ventral surface of the female's 

 thorax between the last three pairs of appendages. This mass contains 

 contorted tubular cavities in which the spermatozoa lie. It is at first 

 white and soft but in a short time turns black and becomes hard. It comes 

 to resemble whalebone in consistency." 



In the epithelium of Panulirus intemiptus, especially in that of the 

 typhlosole-like area (Fig. 24<, i), the finest examples of cilia were ob- 

 served. In this last named region the cilia are very long and extend from 

 the outer surfaces of the cells as well as line the tubules of the glands 

 (Figs. 30 and 31, ^). In cases in which these tubules have been cut 

 across (Fig. 32), the tubular cavity can be seen completely surrounded by 

 epithelial cells (Fig. 32, e), with their long cilia (Fig. 32, h) extending 

 freely into the lumen. 



5. DISCUSSION 



A comparative study of the vasa deferentia of the Decapoda reveals 

 the fact that they are all built on virtually the same plan. There are 

 three more or less well defined regions: (1) an outer protective region, 

 (2) a middle muscular region, and (3) an inner epithelial region. The 

 functions of these will be taken up in logical sequence. 



( 1 ) The outer protective region of the vas deferens serves the pur- 

 pose of protection. In the Brachyura and the Macrura it consists of a 

 single coat of fibrous connective tissue (Figs. 17-21 and 23-25, b), while 

 in the Anomura it is made up of two well defined layers, an outer thin 

 serosa of epithelium (Figs. 11-16, a) and below this is a thicker subserosa 

 of fibrous connective tissue (Figs. 11-16, b). 



(2) The middle muscular region undoubtedly functions in the pas- 

 sage of the spermatophores and the viscid secretions from the interior of 

 the vas deferens to the exterior. In the Brachyura and the Macrura this 

 region is rather thin and consists of a single circular layer of smooth 

 muscle (Figs. 17-21 and 23-25, c). In the Anomura there are two layers 

 of smooth muscle, namely, an outer circular layer (Figs. 11 and 14-16, c) 

 and an inner longitudinal layer (Figs. 11 and 14-16, d). In all probabil- 

 ity the muscular region sets up peristaltic waves along the vas deferens, 

 which force the inner contents of the tube to migrate to the terminal 

 opening where they are expelled to the outside. In the Anomura, since 

 there are two well developed muscular coats, peristalsis must be much 

 more marked than in either the Brachyura or the Macrura. 



