19 



nearly related species two or three different forms of ancestrulse, which as it 

 were represent different stages of the development which these forms have passed 

 through during the lapse of time. The idea that the ascopore, which appears 

 in a number of genera, e. g. in Haplopoma and Microporella, must have arisen 

 from the closure of the sinus in a schizostomous orifice, has several times been 

 expressed, and with this agrees the fact, that Haplopoma impressum (PI. XXII, 

 fig. 9 a) as well as Hapl. cornutiim (PI. XXII, fig. 10 a) have an ancestrula with 

 such an orifice. Neviani^ has found an ancestrula with a similar orifice in 

 Microporella Malusii but in another colony he has found one of Tata-form and in 

 a third the semicircular orifice of the ancestrula was contained in a calcareous 

 region which is surrounded by short spines. A similar variation in the structure 

 of the ancestrula has been found by Jullien- in the genus Hippothoa (Diazeuxia 

 Jullien). Harmer has given a list of 34 different ancestrulae described or pic- 

 tured in the literature, and I may here point out that Smitt has besides pic- 

 tured the ancestrulse of the following species: ^Lepraliai- spathulifera^ Esclia- 

 roides coccinea*, Porella Icevis^, Escharella immersa^, Escb. stenostoma ' and Esch. 

 emucronata *. 



In all the hitherto found ancestrulse with a modified Tata, which belong to 

 ascophorous families with a cryptocyst, there is found a more or less developed 

 depressed cryptocyst, at any rate at the period when they have produced new 

 zooecia, and the existence of this cryptocyst goes to prove, that these families 

 descend from coilostegous forms. That Harmer' at any rate with respect to a 

 part of these forms is of the same opinion is evident from what he says about 

 the cryptocyst in the ancestrula of Escharina vulgaris: »It appears to me to be 

 of great importance to ascertain whether this calcified portion is of the nature 

 of a cryptocyst or not; in other words whether the frontal membrane extends as 

 far as the sharp ridge on the inner side of the base of the spines. I can hardly 

 doubt that this is the case; and if so the Microporoid origin of Escharine forms 

 in which the compensation sac develops as an invagination at the base of the 

 operculum would appear to be indicated*. I may just remark, that Harmer's 

 Microporoid series in all essentials corresponds with my division Coilostega and 

 his Escharine forms with my Ascophora. — Such a transformation from a coilosteg- 

 ous into an ascophorous form as that which Harmer and the author of the pre- 

 sent work advocate, supposes, that the depressed or hollow cryptocyst of the former. 



77 a; * 45, p. 28—34; ' 100, PI. XXVI, fig. 98; ' 100, PI. XXVII. fig. 162, 163; ' 100, PI. XXVI, 

 fig. 109-111; ' 100, Pi. XXVII, fig. 167; 101, PI. XXI, fig. 31; ' 101, PI. XXI, fig. 29; « 101, 

 PI. XXI, fig. 27; ' 18, p. 334. 



2* 



