\20 Systematic guide to the genera and species of Rhizocephala, with anatomical diagnoses. 



by means of a tube opening at the point of fixation into the host and running through the 

 mesentery in the middle line to open into the mantle cavity (mes.can. Piate 8 figs. 10, 12, 

 16, 17 and Text figure 24). I regard this tube which is evidently of purely ectodermal 

 origin and is lined throughout with chitin as representing the invaginated stalk of an ordinary 

 Cirripede, and its probable method of formation and its hearing on the general problem of 

 Ithizocephalan development has been considered at length on pp. 61 and 62. 



I will now give a description of the anato my of Duplorbis which with the help of 

 the figures on Piate 8 (figs. 9 — 19) and of the Text fig. 24 rnay lay a basis for a more com- 

 plete investigation of this important genus. 



In an undissected specimen, represented in two views in Figs. 10 and 11 Piate 8, we 

 can recognize the following parts, firstly, the visceral mass (visc) lying enveloped by the mantle (m), 

 secondly, a linear streak (mes.can) can be observed starting from the stalk of attachment (st) 

 and running about half way round the body in its shortest circumference. This is the mesen- 

 teric canal. In the anterior region where the mesenteric canal ceases, shown in Figure 11, 

 two large discs can be seen lying within the mantle on the visceral mass, these are the two 

 colleteric glands (coli). The position of the mesentery and the fact that the nervous ganglion (gn 

 Text fig. 24) is situated between the two colleteric glands, just in front of the opening of 

 the mesenteric canal into the mantle cavity, give us the clue to the orientation of the body. 

 The morphological antero-posterior axis runs in the actual shortest axis of the body, i. e. 

 through the mesenteric canal, the stalk being at the posterior pole; and the surface carrying 

 the mesenteric canal is, of course, the dorsal surface. The body is therefore immensely late- 

 rally expanded. 



The gross anatomy can be studied by means of the ideal horizontal section given in 

 Text fig. 24. 



The red outlines here indicate the chitinous investments. We see that at the ring or 

 stalk the external chitinous investment of the mantle and the external epithelium are inva- 

 ginated and become continuous with the lining of the mesenteric canal (mes.can) which opens 

 into the mantle cavity (me) just behind the nervous ganglion (#??), and at the anterior edge of 

 the mesentery (mes). 



The two oviduets or colleteric glands (ovd.l., ovd.r.) can be seen on either side of the 

 ganglion, and at either end of the mantle cavity the two bodies are shown described in 

 Chapter 2, which contain spermatozoa and are either complemental males or else very pecu- 

 liarly placed testes (cf). 



The mesentery (mes) represented in the Text fig. 24 by the slanting lines is later- 

 ally expanded, extending posteriorly to the region of the stalk of attachment and anteriorly 

 to the opening of the mesenteric canal which runs in its substance. 



Passing to the minuter structure, the sections on Piate 8 figs. 12 and 14 instruct 

 us that the mantle (m) consists merely of an epithelium which secretes a chitinous membrane, 

 muscles and connective tissue being entirely absent. The surface of the visceral mass is 



