I5â ^- GOTO. 



shape of the hooks ah'eiidy described, and the raised part chitinised.'^ 

 It should, however, he oloserved that tlie process of absorption has pro^ 

 bably played as much part in the forniatiijn of the hooks as that of 

 chitinisation. 



The penis in Octoeotijle is essentially similar to that in DidUlophora, 

 but its hooks are more like the atrial spines of M'lcrocolijle. In Onclio- 

 cotijlc the penis is nothing else than a mass of elastic connective tissue 

 around the terminal porti(3n of the vas deferens, which is separated 

 from the surrounding mesenchyma Ijy a mendjrariC, and is therefore 

 essentially similar to that of Diclidopliora. The hooks are, however, 

 totally absent. 



The atrial spines of Microcotijlc are, as already described, formed 

 by local, conical elevations and chitinous transformation of the lining 

 membrane of the genital atrium, and are therefore homologous in a 

 broad sense with the chitinous penis and penis hooks of other genera 

 as well as with the hooks which are present in many genera in the 

 posterior sucker or in the posterior part of the body, and with the 

 local chitinous areas of the lining membrane of the suckers (PI. VI, 

 fig. 4; 1^1. XII, fig. 4). I also believe that the chitinous frame-work 

 of the suckers of many genera is homologous with tlie structures just 

 menti(3ned, /. c, that it is a product of the local transformation of 

 the investing membrane of the body. 



The homologue of the }>enis of 2I.onocolijlc and Hcxacotijle and 

 therefore of Tristomum can als(3 be tniced in Microcolijle. It has already 

 been st.ated that in some species of this genus, as M. fusiform is (PI. Y, 

 fig. 1), ])/. caudata (fig. 3), and il/, schastis (PI. A'l, fig. 1), the vas 

 deferens opens at the top of a conical papilla projecting into the genital 

 atrium. This pajûlla is, in my opinion, the homologue of the penis. 



1). Here I have for couveuienco used a false expression. In point of fact the process 

 of raising and that of chitinisation probably proceeed simultaneously. 



