136 LACINULARIA SOCIALIS 



clear space ; isolated by crushing the ovum it is a transparent, 

 colourless vesicle. 



The perfect ova are oval, about i-ioth inch in diameter, and are 

 extruded by the parent into the gelatinous connecting substance,, 

 where they undergo their development (fig. 11). 



The changes which take place after extrusion, or even to some 

 extent within the parent, are — i, the disappearance of the germinal 

 vesicle (as I judge from one or two ova in which I could find none) ; 

 2, the total division of the yolk, as described by Kolliker in Megalo- 

 trocha, until the embryo is a mere mass of cells, from which the 

 various organs of the foetus are developed (figs. 12, 13, 14, 15, 16). 



The youngest foetuses are about i-7oth of an inch in length. The 

 head is abruptly truncated, and separated by a constriction from the 

 body : a sudden narrowing separates the other extremity of the 

 body from the peduncle, which is exceedingly short, and provided 

 with a ciliated cavity, a sort of sucker, at its extremity. The head is 

 nearly circular, seen from above, and presents a central protuberance 

 in which the two eye-spots are situated. The margins of this protu- 

 berance are provided with long cilia — it will become the upper circlet 

 of cilia in the adult. 



The margin of the head projects beyond this, and is fringed with a 

 circlet of shorter cilia : this is the rudiment of the lower circlet of 

 cilia in the adult. The internal organs are perceived with difficulty ; 

 but the three divisions of the alimentary canal, which is as yet straight, 

 and terminates in a transparent cloaca, may be readily made out. 

 The water-vascular canals cannot be seen, but their presence is 

 indicated by the movement of their contained cilia here and there 



(fig- I7> 



In young LacimilaricB, i-30th of an inch in length, the head has 

 become triangular, the peduncle is much elongated, and thus it 

 gradually takes on the perfect form (fig. 18). The young had 

 previously crept about in the gelatinous investment of the parents ; 

 they now begin to " swarm," uniting together by their caudal extremi- 

 ties, and are readily pressed out as united free swimming colonies,, 

 resembling, in this state, the genus Conochilus. 



The process of development of these ova is therefore exactly 

 that which takes place in all fecundated ova, and would lead 

 one to suspect that spermatozoa should be found somewhere or 

 other. 



Now, from the observations of Mr. Dalrymple, we should be led to 

 seek a distinct male form with the ordinary spermatozoa. From 

 those of Kolliker, on the other hand, we should equally expect to find 



